Republican hawks were Barack Obama’s foil in 2007 and 2008. They may prove his salvation in 2009 and 2010.

Obama’s opposition to the war in Iraq and those who supported it made him the darling of the Democratic base, and turbocharged his drive to the White House. As a candidate for president, he repeatedly condemned the war as a fiasco and declared that President Bush’s “surge” would not only fail to improve conditions in Iraq, but would actually make them worse. In August 2007, when his rival Hillary Clinton told the Veterans of Foreign Wars that the surge appeared to be working, Obama maintained that the war was as futile as ever. As The New York Times headlined its story the next day: “Obama Sees a ‘Complete Failure’ in Iraq.”

But the antiwar liberals who adored Obama the candidate when he vowed to pull the plug on the war in Iraq are not nearly as enamored of Obama the president when he calls for enlarging the war in Afghanistan.

Last month, speaking once again to a VFW convention, Obama reiterated his commitment to a withdrawal from Iraq. The troops will be out by the end of 2011, he said, “and for America, the Iraq war will end.” But the war in Afghanistan, where American troops have been dying in record numbers, will go on.

“This is a war of necessity,” the president insisted - “not only a war worth fighting,” but one “fundamental to the defense of our people.” He warned that “those who attacked America on 9/11 are plotting to do so again,” and that “if left unchecked, the Taliban insurgency will mean an even larger safe haven from which Al Qaeda would plot to kill more Americans.” Earlier this year Obama ordered 21,000 additional US personnel to Afghanistan. By year’s end, troop levels there will be at 68,000 - the most ever - and General Stanley McChrystal, the theater commander, is thought to be on the point of asking for more.

But doubling down on the war - in effect, committing himself to an Iraq-like “surge” - will drive a wedge between Obama and the antiwar left that once acclaimed him.

Two recent national polls show plummeting support for the war. In a Washington Post-ABC News survey, 51 percent of the public says the conflict in Afghanistan is “not worth fighting,” and only 24 percent is willing to send more troops. A CNN/Opinion Research poll finds even wider opposition to the war - 57 percent, the highest since US involvement in Afghanistan began.

Drill down into those numbers, however, and you find a gaping partisan/ideological divide. “Majorities of liberals and Democrats alike now … solidly oppose the war and are calling for a reduction in troop levels,” the Post observes. By contrast, Republicans and conservatives “remain the war’s strongest backers.” A majority of conservatives not only supports the war but even approves Obama’s handling of it. The CNN poll puts Republican support for the war at 70 percent, as against the 74 percent of Democrats and 57 percent of independents who are opposed.

On Capitol Hill, Democrats are beginning to distance themselves from Obama on the war. Wisconsin Senator Russ Feingold, claiming that “our military presence in Afghanistan may be undermining our national security,” wants the troops withdrawn. Massachusetts congressman Jim McGovern complains that “we’re getting sucked into an endless war here.” Two Democrats on the Senate Armed Services Committee - the chairman, Carl Levin of Michigan, and Jack Reed of Rhode Island - are signaling that any request for more troops “probably will run into resistance,” the AP reported over the weekend.

Republicans, on the other hand, have publicly let the president know that while they may oppose him on other issues, he can count on their support if he pursues victory in Afghanistan. “Stand strong, Mr. President,” urged the Republican National Committee in a statement posted on its website and distributed by e-mail. Explain “why the voices of defeat are wrong.”

The success of the Obama presidency likely depends on Afghanistan, and to achieve victory there the president will need the help of the very Republicans he and his backers so often attacked for pursuing victory in Iraq. Now those backers are backing away, while the GOP acts as an honorable and loyal opposition. Politics may not be fair, but it sure is ironic.