Barack Obama and John McCain took the gloves off Monday, one day before the final two Democratic primaries are expected to put Hillary Clinton down for the count and launch the start of a grueling general election campaign.

The presidential primary season ends Tuesday night with Democratic votes in Montana, Republican votes in New Mexico and votes in both parties in South Dakota.

McCain, who in March locked up the delegates he needs to win the Republican nomination, is planning to deliver a primary night speech -- his first in months -- in which he will likely recognize that his opponent in November will be the senator from Illinois.

But even as Obama approaches the threshold needed to defeat Clinton, he and McCain are trading blows. With 31 delegates at stake Tuesday, Obama will need to pick up about 15 superdelegates in order to declare victory.

The narrative shaking itself out for the general election is a traditional old school vs. new school argument. Obama says McCain represents the policies of the past and is old not only in years, but in thinking and outlook. McCain counters by borrowing a line from Ronald Reagan, saying he doesn't want to hold Obama's youth and inexperience against him, but the Democrat is untested and not ready to be the leader of the free world.

On Monday, McCain continued that theme, ridiculing Obama for his willingness to meet with Iranian President Mahmoud Ahmadinejad, telling the American-Israel Public Affairs Committee that such a meeting would be a "spectacle" that would embolden extremists.

"It's hard to see what such a summit with President Ahmadinejad would actually gain, except an earful of anti-Semitic rants, and a worldwide audience for a man who denies one Holocaust and talks before frenzied crowds about starting another," McCain said. "Such a spectacle would harm Iranian moderates and dissidents, as the radicals and hardliners strengthen their position and suddenly acquire the appearance of respectability."

Afterward, at a town hall meeting in Michigan, Obama said McCain would continue the policies of President Bush by leaving troops in Iraq for four more years.

"There's a reason the problems we face today are so much bigger than they were several years ago," Obama said. "A big part of it is that George Bush and John McCain have been so focused on pursuing a flawed and costly war in Iraq that they’ve lost sight of our mounting problems here at home. Instead of working to fix our economy and lift up hardworking families, they’ve fought to extend a war that’s costing thousands of lives and billions of dollars without making us any safer -- a war that has strengthened our enemies and distracted us from the real battle with Usama bin Ladin in Afghanistan and Pakistan."

McCain, who has often berated Obama for saying in the Democratic debates that he would negotiate with Ahmadinejad and other U.S. foes, said the Illinois senator doesn't understand that the U.S. should not foster a relationship with a country pursuing nuclear weapons for use against U.S. allies.

"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, adding that Obama is engaging in a “serious misreading of history.

The Arizona senator proposed a new approach to sanctions, suggesting that severely limiting Iranian imports of gasoline, targeted sanctions such as denying visas and freezing assets, and calling on the international community to divest itself from Iran the way it did in South Africa in an effort to end apartheid.

AIPAC'S members plan to lobby for sanctions against gasoline imports on Capitol Hill this week. McCain said he U.S. should work toward this goal if the U.N. Security Council fails to issue tougher sanctions.

"“Rather than sitting down unconditionally with the Iranian president or supreme leader in the hope that we can talk sense into them, we must create the real-world pressures that will peacefully but decisively change the path they are on,”" McCain said.

Obama, who has since said he would not just dive into a room feet first with Ahmadinejad and other terror sponsors, counters that McCain's refusal to negotiate at all would make the U.S. and Israel less secure.

McCain "promises sanctions that the Bush administration has been unable to persuade the Security Council to deliver," said his campaign spokesman Hari Sevugan.

"He promises a divestment campaign, even though he refused to sign on to Barack Obama's bipartisan divestment bill, refused to get his colleagues to lift an anonymous hold on the bill, and willfully ignores the fact that trade and investment between Iran and Iraq continue to expand. He stubbornly refuses to engage in aggressive diplomacy, ruling it out unconditionally as a tool of American power," Sevugan said in a "pre-buttal" to McCain's speech.

Speaking to the pro-Israel lobby, one of the more influential in Washington, McCain urged financial sanctions on the Central Bank of Iran, which he said aids in terrorism and weapons proliferation, and he took a shot at Obama for his vote last fall against designating the Iranian Revolutionary Guard Corps as a terrorist organization, mocking him for not supporting the bill.

"“He opposed this resolution because its support for countering Iranian influence in Iraq was, he said, a 'wrong message not only to the world, but also to the region,'" McCain said. "But here, too, he is mistaken. Holding Iran's influence in check, and holding a terrorist organization accountable, sends exactly the right message -- to Iran, to the region and to the world."

FOX News' Mosheh Oinounou and The Associated Press contributed to this report.