The latest Democrat to enter the 2020 presidential race, former Pennsylvania congressman Joe Sestak, brings the primary field to 25 candidates.
The candidates in the sprawling field range in age from 37 to 89 and include liberals and moderates; senators, governors and mayors; and an unprecedented number of women and minorities.
Democrats view the upcoming election as a must-win, and they're looking to nominate someone who is their best hope to beat President Donald Trump.
Here are the candidates:
Best known for: The senator from Colorado gave a scorching speech slamming Republican Sen. Ted Cruz of Texas during the recent government shutdown.
Biggest strength: Bennet is viewed as a wonky, issue-oriented pragmatist who has won tough campaigns, which could be a winning combination for Democratic voters who don't want to veer too far left but are eager to beat Trump.
Biggest weakness: Bennet is not as well known as many other senators competing for the Democratic nomination and has no natural base.
Best known for: Being former President Barack Obama's vice president from 2009 to 2017 and U.S. senator from Delaware from 1973 to 2009.
Biggest strength: He's well-known nationally and popular in some places Democrats have lost recently, such as working-class swing states Wisconsin, Michigan and Pennsylvania, his birthplace.
Biggest weakness: Biden would be the oldest person ever elected president, with a nearly five-decade record for opponents to comb through, at a time many in his party are clamoring for a new generation to take the reins. The notoriously chatty former senator also tends to commit verbal gaffes and faced recent accusations by some women of uninvited, though nonsexual, touching.
Best known for: Serving as mayor of Newark and, currently, U.S. senator from New Jersey. He made headlines last year during his self-proclaimed "'I am Spartacus' moment" as he flouted Senate rules against disclosing confidential documents during Brett Kavanaugh's Supreme Court confirmation fight.
Biggest strength: His optimistic, unity-first attitude could resonate at a time of deep political divisions.
Biggest weakness: Trying to convince voters that he's tough enough to take on Trump.
Best known for: Serving as governor of Montana since 2013
Biggest strength: He's the only statewide elected official in the field who has won a state that President Donald Trump carried in 2016.
Biggest weakness: Low name recognition as the chief executive of one of the least-populated U.S. states as well as raising enough money and getting enough support in polls to qualify for Democrats' first debates in June.
Best known for: Serving as mayor of South Bend, Indiana.
Biggest strength: He's won over voters and many skeptics with his intelligence and an articulate yet plain-spoken speaking style. He's also shown an ability to inspire voters of different ages with a message of hope and "a new generation of leadership" and has been able to raise millions more than many of his Democratic rivals.
Biggest weakness: His youth and lack of political experience — his only public office has been leading the community of about 100,000 people — will give some voters pause. He also will need to ramp up his campaign operations and do more to appeal to minority voters in order to maintain his early momentum.
Best known for: Serving as Housing and Urban Development secretary during President Barack Obama's second term and as the mayor of San Antonio, Texas, for five years.
Biggest strength: His youthfulness and status as the only Latino in the race could help him win the votes of Democrats looking for a new face of their party.
Biggest weakness: His fundraising lags well behind other contenders.
BILL DE BLASIO
Best known for: Serving as New York City's mayor since 2014.
Biggest strength: The leader of the nation's biggest city will be able to cite accomplishments such as expanding full-day prekindergarten citywide and curtailing police tactics that critics said were discriminatory, while presiding over continued drops in violent crime.
Biggest weakness: He faces skepticism even at home, with a recent poll finding 76% of New Yorkers say they believe he shouldn't run. He could also face obstacles in trying to distinguish himself in a field crowded with left-leaning Democrats.
Best known for: Being a former congressman from Maryland.
Biggest strength: He has rolled out a rural-focus policy that includes proposals to strengthen family farmers and rural infrastructure, a plan that could play well in the battleground Rust Belt states won by Trump.
Biggest weakness: Low name recognition.
Best known for: Serving as a U.S. representative for Hawaii, the first American Samoan and first Hindu to be elected to Congress.
Biggest strength: Her military service in Iraq and Kuwait with the Hawaii National Guard.
Biggest weakness: She has been criticized for traveling to Syria in 2017 to meet with Syrian President Bashar Assad, who has been accused of war crimes and even genocide. She was also forced to apologize for her past work advocating against gay rights.
Best known for: The senator from New York is one of her chamber's most vocal members on issues of sexual harassment, military sexual assault, equal pay for women and family leave.
Biggest strength: Not being afraid to defy her own party in the #MeToo era, calling early for Democratic Sen. Al Franken's resignation over sexual misconduct allegations and saying Bill Clinton should have voluntary left the presidency over an affair with intern Monica Lewinsky.
Biggest weakness: Sluggish campaign fundraising in the wake of some unpleasant #MeToo headlines of her own, with Gillibrand acknowledging there were "post-investigation human errors" made when her Senate office investigated allegations of sexual misconduct against various staffers.
Best known for: Serving as U.S. senator representing Alaska from 1969 to 1981 who read the Pentagon Papers into the congressional record. He also ran for president unsuccessfully in 2008, first as a Democrat and then as a Libertarian.
Biggest strength: Long antiwar record, which could play well with the progressive wing of the party.
Biggest weakness: Oldest candidate in the race by far. Gravel's campaign has previously said he wanted to make the debate stage in an effort to push the party to the left, not to win.
Best known for: The former California attorney general is now the junior U.S. senator from California, known for her rigorous questioning of Trump's nominees.
Biggest strength: As the one black woman in the race, she's able to tap into networks like historically black colleges and universities and her Alpha Kappa Alpha sorority that haven't been fully realized before.
Biggest weakness: Her prosecutorial record has come under scrutiny amid a push for criminal justice reform.
Best known for: The former Colorado governor was a quirky brewpub owner who became a politician late in life.
Biggest strength: An unorthodox political persona and successful electoral track record in a swing state. He's one of the few governors in a race heavy with senators and D.C. stalwarts.
Biggest weakness: He's previously joked that he was too centrist to win the Democratic nomination. As governor he disappointed some environmentalists by not regulating the energy industry more. He's another white male baby boomer in a party filled with younger and more diverse candidates that better reflect its base.
Best known for: Being governor of Washington state and a former congressman.
Biggest strength: His campaign emphasis is on combating climate change, which he frames as an economic opportunity in addition to a moral imperative.
Biggest weakness: He risks being labeled a one-issue candidate.
Best known for: The three-term Minnesota senator raised her national profile during a Senate committee hearing for Supreme Court nominee Brett Kavanaugh when she asked him whether he had ever had so much to drink that he didn't remember what happened. He replied, "Have you?"
Biggest strength: She's known as a pragmatic lawmaker willing to work with Republicans to get things done, a quality that's helped her win across Minnesota, including in rural areas that supported Trump in 2016. She says her Midwestern sensibilities would help Democrats reclaim critical battlegrounds like Wisconsin and Michigan.
Biggest weakness: Her pragmatism may work against her in a primary, as Democratic voters increasingly embrace more liberal policies and positions. There have also been news reports that she has mistreated staff.
Best known for: Serving as the mayor of Miramar, Florida, and playing on the Florida State University Seminoles' 1993 national championship football team.
Biggest strength: He touts his mayoral experience balancing government regulations needed to protect the environment while allowing room for companies to prosper.
Biggest weakness: Low name recognition and funding.
Best known for: The Massachusetts congressman and Iraq War veteran gained national attention for helping lead an effort within the party to reject Nancy Pelosi as House speaker after Democrats regained control of the chamber.
Biggest strength: Military and congressional experience.
Biggest weakness: Low name recognition, late start on the fundraising necessary to qualify for the summer debate stage.
Best known for: The former three-term congressman narrowly lost the 2018 Senate race to Republican Ted Cruz in Texas, the country's largest conservative state.
Biggest strength: A do-it-yourself campaign style that packs lots of travel and multiple events into long days and encourages off-the-cuff discussions with voters that still allow O'Rourke to talk up his days as a onetime punk rock guitarist and his love for his home on the U.S.-Mexico border.
Biggest weakness: He's longer on enthusiasm and vague, bipartisan optimism than actual policy ideas, and the style-over-substance approach could see O'Rourke's strong early fundraising slip once the curiosity begins to fade.
Best known for: The Ohio congressman made an unsuccessful bid to replace Nancy Pelosi as House Democratic leader in 2016.
Biggest strength: Ryan has touted himself as a candidate who can bridge Democrats' progressive and working-class wings to win the White House.
Biggest weakness: Low name recognition, late start on grassroots fundraising.
Best known for: The senator from Vermont's presidential primary campaign against Hillary Clinton in 2016 laid the groundwork for the leftward lurch that has dominated Democratic politics in the Trump era.
Biggest strength: He generated progressive energy that fueled his insurgent 2016 campaign and has the best fundraising numbers of any Democrat so far.
Biggest weakness: Expanding his appeal beyond his largely white base of supporters.
Best known for: The former congressman from Pennsylvania went against party elders, including Obama and Biden, and challenged Republican-turned-Democratic Sen. Arlen Specter in the state's 2010 Democratic primary, which Sestak won before losing the general election to Republican Pat Toomey.
Biggest strength: He is known as a tireless campaigner and has decades of national defense experience in the Navy.
Biggest weakness: His go-it-alone campaign strategy in 2010 and again in 2016 sowed deep resentments by Democratic Party leaders in Washington and Pennsylvania. He has been out of public office since 2010, and his public speaking style can come across as stilted and affected.
Best known for: The California congressman is a frequent guest on cable news criticizing President Donald Trump.
Biggest strength: Media savvy and youthfulness could appeal to young voters.
Biggest weakness: Low name recognition, late start on grassroots fundraising.
Best known for: The senator from Massachusetts and former Harvard University law professor whose calls for greater consumer protections led to the creation of the Consumer Financial Protection Bureau under President Barack Obama.
Biggest strength: Warren has presented a plethora of progressive policy ideas, including eliminating existing student loan debt for millions of Americans, breaking up farming monopolies and mammoth technology firms, implementing a "wealth tax" on households with high net worth and providing universal child care.
Biggest weakness: She is viewed as one of the most liberal candidates in the Democratic field, which could hurt her among moderates. Her policy-heavy approach also risks alienating voters at a time when other candidates are appealing to hearts as much as to minds.
Best known for: Best-selling author and spiritual leader.
Biggest strength: Outsider who could draw interest from voters who are fans of her books.
Biggest weakness: Low name recognition, little political experience.
Best known for: Entrepreneur who has generated buzz with his signature proposal for universal basic income to give every American $1,000 a month, no strings attached.
Biggest strength: Robust policy agenda, tech savvy.
Biggest weakness: Low name recognition, no political experience.