FRANKLIN, Kentucky (AP) -- In one of the country's most expensive and contentious Senate races, Democrat Alison Lundergan Grimes, Kentucky's secretary of state, and Republican Sen. Mitch McConnell, the Senate Minority Leader, both hold big leads over their opponents in Tuesday's primary contests, a dress rehearsal for November's showdown in a key race that could determine control of the Senate and the fate of President Barack Obama's agenda in the last two years of his second term.
The Kentucky race is among a dozen nationally that will help determine control of the Senate. Republicans need to gain just six seats to claim a majority and they cannot afford to lose the Kentucky seat they now hold -- one of the few opportunities for a Democratic pickup. Polls show McConnell and Grimes in a dead heat.
A McConnell win could help swing control of the Senate to the Republicans, setting up two years of intense fighting on the future of the nation's health care law -- Obama's signature legislative achievement. A Democratic win would topple a 30-year Republican incumbent and Senate leader.
Grimes and McConnell have already raised a combined $19 million in the two years leading up to Tuesday's primary elections.
On Saturday, Grimes and McConnell were both campaigning near the town of Franklin.
McConnell told a group of about 30 people at the Tanglewood Farms Market & Deli that the Kentucky Senate race was a microcosm of the national political discussion.
"We will be in the crosshairs of this great national debate about what American ought to be like," McConnell said. "Do we want to be like western European countries, with big debt, high taxes, strangulated regulations? Or do we want to be a country that's still based on opportunity and initiative and the chance to realize your dream without the government trying to micromanage every aspect of your life."
In this small Kentucky town near the Tennessee border, where registered Democrats outnumber registered Republicans by 2 to 1, Grimes and McConnell had the same message: change. Grimes would like to see Kentucky change senators, and she criticized McConnell for voting against raising the minimum wage and blocking measures to ensure women make the same salaries as men.
McConnell would like to stay in the Senate, but change jobs, from minority leader to majority leader. As majority leader he'd be in charge of stopping a president's agenda that he says has devastated Kentucky's coal industry and upended the country's health care system.
McConnell and his allies are already running television ads comparing Grimes to Obama, whose disapproval rating in Kentucky is at least 60 percent. But polls show that McConnell's disapproval rating is just as high if not higher than the president's.
"Nothing about this election is going to change who the president is," Grimes said in an interview, calling herself a "fierce opponent" to Obama's new emission standards for coal-fired power plants, a big issue in Kentucky's coalfields. "But Kentuckians do realize that we can finally change who is in Washington, D.C."
With minimal opposition, Tuesday could likely be a victory for Grimes as she seeks to rally her base heading into November. But the primary is tricky for McConnell, who has a comfortable lead over Louisville businessman Matt Bevin but could lose some 30 percent of Republican voters to other Republican candidates. Conservatives are unhappy about McConnell's compromises with Democrats to raise the debt ceiling, pass the Wall Street bailouts and other fiscal issues. Bevin is relying on support from the conservative anti-tax, limited government tea party movement.
"I think he'll have a very tough time bringing them back," said Jonathan Hurst, Grimes' campaign manager. "We will welcome those who vote against Sen. McConnell and his own party on Tuesday to join our campaign."
But Republicans in Franklin were confident that the changing political demographics of their county -- with a preference for Democratic state officials and Republican federal officials -- would be emblematic of the state as a whole in November.
"When I first ran for office in '98, party registration for Democrats was at that time about 5 to 1. ... It's almost dropped to 2 to 1," said Jim Henderson, a Republican and the county's top elected official. "It's because the national Democratic Party doesn't reflect even Kentucky Democrats who might consider themselves conservative."
The other key primary Tuesday is in another southern state, Georgia, for the Senate seat left open when Republican Sen. Saxby Chambliss announced his retirement. The Republican primary appears likely to result in a runoff since there are five major candidates in the race -- U.S. Reps. Paul Broun, Jack Kingston and Phil Gingrey, former Georgia Secretary of State Karen Handel, and businessman David Perdue, the former CEO of the Dollar General discount store chain.
In the primary campaign's final debate on Saturday, Perdue, who has been leading in polls, sought to explain comments he made earlier this week about how cutting spending and increasing revenue are both needed to address the nation's fiscal problems. His chief rivals have used those comments to accuse him of supporting tax increases -- which is anathema to Republican base voters.
On the Democratic side, Michelle Nunn, the daughter of former Georgia Sen. Sam Nunn, is likely to advance in her primary against three lesser-known candidates. Polls show her running a close race with the leading Republican contenders in what may be the only other Democratic Senate pickup opportunity.
Most of the attention in November will be on the battle for control of the Senate because Republicans appear likely to maintain control of the House of Representatives. Republicans are pinning their hopes for gaining a Senate majority on states such as Alaska, North Carolina, Louisiana, West Virginia and Montana where Democrats must defend seats in states carried by Republican Mitt Romney in the 2012 presidential race.
Associated Press writers Adam Beam in Franklin, Kentucky, and Christina A. Cassidy in Buford, Georgia, contributed to this report.