John McCain and Barack Obama are using the foreign policy challenge of a rising Iran to play up what each describes as the other's weaknesses _ inexperience or recklessness on Obama's part and McCain's embrace of failed tactics.
That Iran is a campaign issue at all this year _ with U.S. troops fighting next door in Iraq and U.S. voters focused on rising gasoline prices _ is a measure of the spreading influence and deadly potential of the main U.S. rival in the Mideast.
The debate so far has mostly concerned a false choice: whether or not to talk to Tehran. The political exchanges have obscured what is probably the next president's largest foreign policy challenge, other than the next step in Iraq.
Somehow, some way, the next U.S. president is going to have to confront Iran. Unless there is war, that will almost certainly mean some kind of talking. It may not be face-to-face, as Obama would entertain, but the Republican and Democratic candidates both say diplomacy is the preferred path.
The candidates define their Iran policy partly by their differing positions on the unpopular Iraq war, and partly by a tactical difference on when or how to negotiate with Tehran.
Obama argues that McCain is advocating the same Iran policy as President George W. Bush and that the hands-off approach has failed and only expanded Iran's sway. McCain argues that Obama is naive to think he can talk Iran into better behavior.
"We hear talk of a meeting with the Iranian leadership offered up as if it were some sudden inspiration, a bold new idea that somehow nobody has ever thought of before," McCain said Monday at the American Israel Public Affairs Committee.
Two days later, Obama told the same audience:
"Contrary to the claims of some, I have no interest in sitting down with our adversaries just for the sake of talking. But as president of the United States, I would be willing to lead tough and principled diplomacy with the appropriate Iranian leader at a time and place of my choosing if, and only if, it can advance the interests of the United States."
Obama has said strong presidents talk to their enemies, including the Soviet Union which posed a greater threat to the United States than Iran.
Obama points out that Iran's influence and ambitions expanded during the Bush administration. U.S.-led invasions toppled regimes in Afghanistan and Iraq that were hostile to the West but also had served as counterweights to Iran.
Both McCain and Obama talk primarily of Iran as a threat, although neither rules out that narrowing a three-decade rift could serve U.S. interests.
Both say Iran is a danger to U.S. forces in Iraq and must be deterred. Both say Iran represents a wider threat to the region, particularly U.S. ally Israel, and perhaps beyond. They say Iran must not be permitted to develop nuclear weapons, and accuse Tehran of seeding and funding terrorism.
That's the basic assessment held by the Bush administration and much of the rest of the world, so it's no surprise McCain and Obama share it.
It's more surprising they would use such a similar mix of diplomacy, pressure tactics and the implied threat of American military might to keep the mullahs in check.
Both men would tinker with the basic carrot-and-stick policy that Bush settled on fairly late in his tenure, and which has so far failed to move Iran off a presumed ambition for nuclear weapons.
Obama would make more changes than McCain, chiefly lifting a precondition to direct U.S.-Iran negotiations that Iran finds insulting and unacceptable. The Bush administration demands that Iran shelve its enrichment of uranium before the United States joins European negotiators already talking to Iran about its nuclear program or holds broad nation-to-nation talks.
McCain hopes to rely on diplomacy and coercion to head off what he says is an unacceptable Iranian drive for the bomb. He says, as do Bush and Obama, that deadly force is a last resort.
More memorable, perhaps, was a moment early in the campaign when McCain jokingly sang "bomb-bomb-bomb, bomb-bomb Iran," to the tune of the Beach Boys hit "Barbara Ann."
On Monday, the Republican called for sanctions on Iranian imports of gasoline and on the Central Bank of Iran, denying visas and launching a worldwide campaign to get businesses, pension funds and financial institutions to divest their holdings in companies that do business with Iran.
McCain's proposed sanctions go somewhat beyond what Bush has pursued, but are in keeping with the strategy of using Iran's financial and economic dealings as leverage. That strategy requires cooperation with nations that, unlike the U.S., have meaningful economic ties to Tehran.
McCain would continue current U.S. policy of using the U.N. Security Council to press Iran to give up the most troublesome aspects of its nuclear program. That means that both global sanctions and the offer of negotiations would be on the table, so long as the Security Council's other permanent members insist on that dual approach.
McCain does not rule out U.S. face-to-face discussions with Iran but says a presidential-level meeting would be counterproductive.
"Such a spectacle would harm Iranian moderates and dissidents as the radicals and hard-liners strengthen their position and suddenly acquire the appearance of respectability," McCain said.
Obama proposes what his campaign calls "aggressive diplomacy," that unifies piecemeal outreaches to Iran in a clear menu of incentives and punishments.
Current sanctions would stand, and Obama would consider additional ones plus international diplomatic pressure to bring Iran to the bargaining table and end Iran's alleged support for terrorist groups.
His campaign says that while there are no bold new offers proposed now, the Bush administration has never made the effort required to sell even the current offer as a good deal for Iran.