Obama made history Tuesday by becoming the first black nominee of a major U.S. political party, a victory on a promise of hope and change for Americans weary of economic turmoil and years of war.

His battle against McCain, a veteran senator who effectively clinched the Republican nomination months ago, looks to be a clash of generations as well as a debate on Iraq. Obama, 46, opposes the war; McCain, 71, is a former Vietnam prisoner of war and staunch supporter of the current U.S. military mission.

The Democratic presumptive nominee, addressing the American Israel Public Affairs Committee on Wednesday, criticized McCain for supporting a "plan for staying, not a plan for victory" in Iraq.

"Keeping all of our troops tied down indefinitely in Iraq is not the way to weaken Iran, it is precisely what strengthened it," Obama, who made history Tuesday by becoming the first black to win the nomination of a major U.S. political party, told the pro-Israel lobby group, known as AIPAC.

In securing the delegates needed to win, Obama completed one of the most remarkable U.S. political campaigns in memory. A first-term senator, unknown nationally four years ago, he toppled one of America's most powerful political families.

Clinton, seeking to become the first female president, had long been seen as the inevitable nominee, and their battle fractured the Democrats' ranks while McCain has had since March to lay the groundwork for the Republicans' White House run.

Obama's victory was a milestone for a nation where, just decades ago, racial discrimination was so severe blacks in some states could not eat at the same lunch counters as whites, and many had to fight just for the right to vote.

His accomplishment drew the attention of Condoleezza Rice, a Republican and the first black secretary of state in history, who said the Democrat's victory was an "extraordinary expression" that the first words of the U.S. Constitution, "'We, the people' is beginning to mean all of us."

White House spokeswoman Dana Perino also extended President George W. Bush's congratulations, though Bush did not call Obama.

Obama's comments to AIPAC came as two fellow senators -- Tom Harkin of Iowa and Ken Salazar of Colorado -- threw their support behind him after remaining neutral through the 17-month nomination battle with Clinton.

Walter Mondale, a Clinton supporter who served as vice president under Jimmy Carter, also announced he was backing Obama.

In terms of electoral math, their endorsements hardly mattered as Obama had more than enough to prevail at the party convention in Denver in August.

But Mondale, Harkin, Salazar and others poised to endorse Obama later in the day were also sending a message to Clinton that her race is over, whether she will admit it or not. Four top Democratic officials sent a similar message earlier in the day, issuing a joint statement urging uncommitted superdelegates to make their choice clear by Friday so that the party can unify ahead of the general election.

The former first lady has yet concede defeat although she is courting an invitation from Obama to become his vice presidential running mate.

Clinton followed Obama to the podium at AIPAC, delivering a strong defense of Israel -- and also of her rival, saying to applause: "Let me be very clear. I know that Senator Obama will be a good friend to Israel."

While she made no mention of her future plans, her aides were not as reticent.

"I think a lot of her supporters would like to see her on the ticket," Clinton campaign chairman Terry McAuliffe said.

But Obama spokesman Robert Gibbs cautioned "there is no deal in the works."

"When the dust settles and it makes sense for her, he'll meet whenever she wants to," Gibbs said. "She's accumulated a lot of votes throughout this country. We want to make sure that we're appealing to her voters."

On the final night of the primary season, Clinton won South Dakota while Obama took Montana -- and a slew of party superdelegates who declared their support to help him clinch the party nod. He did it, according to The Associated Press tally, based on primary elections, state Democratic caucuses and support from superdelegates. It took 2,118 delegates to clinch the nomination, and Obama had 2,144 by the AP count.

Pennsylvania Gov. Ed Rendell, a dogged Clinton supporter, summed it up by saying that the race "is over."

The primaries behind them, McCain and Obama were wasting no time drawing the battle lines for the November election, which will make history with the election of either the oldest first-term president or the first black leader.

The Republican was taking his message -- that he has a record of reform while his opponent simply has rhetoric -- directly to the voters in television interviews from Louisiana, where he will campaign later Wednesday.

He again argued that Obama was inexperienced, and had "exercised very bad judgment on national security issues and others."

On Wednesday, McCain challenged Obama to join him in 10 town hall meetings with voters between now and the Democratic National Convention in August, with the first proposed for June 12 in New York.

Obama, speaking Tuesday night in St. Paul, Minnesota -- where the Republican convention will be held in September -- ceded no ground on the reformer mantle and cast McCain as a continuation of Bush's unpopular eight-year tenure.

In his speech at AIPAC, Obama urged his audience to reject what he said were false e-mails circulating about him, stressed his support for Israel and depicted the war in Iraq as a threat to Israel's security, which he described as "sacrosanct."

He backed a Palestinian state that is "contiguous and cohesive," but also said any agreement must "preserve Israel's identity as a Jewish state, with secure, recognized and defensible borders. Jerusalem will remain the capital of Israel, and it must remain undivided," he said.

Obama said Bush's decision to invade Iraq had enabled the hardliners in Iran to tighten their grip on power, leaving both the United States and Israel less secure.

McCain "offers a false choice: stay the course in Iraq or cede the region to Iran. ... It is a policy for staying, not a policy for victory," Obama said, adding he favors a phased withdrawal of troops from Iraq.