Sgt. Cole Reece, a Task Force Shadow flight medic for the 101st Airborne, runs through a dusty field in search of soldiers wounded in a blast in Kandahar. (Linda Davidson/THE WASHINGTON POST)

Barbour, until Tuesday a presidential contender, questioned the purpose of the war in multiple public appearances. "I think it is time for the administration to take a step back to look at what we're doing there," Barbour told the New Hampshire Union-Leader. "And if the mission is nation-building, the American people need to be told that in a very straightforward way.” A few days later, he told Republicans in Iowa, “We need to step back in Afghanistan, and we need to decide whether the resources we’re putting into Afghanistan, 110,000 soldiers and about $2 billion a week, are essential for our mission.”

Other Republicans have criticized President Obama’s handling of the war. But few have questioned the mission itself or the resources devoted to it. Conventional wisdom argues that it’s dangerous for Republicans to oppose a war, especially one launched by former President Bush and led by General David Petraeus.

“I'd say one of the big ‘surprises’ coming up in the GOP primary will be the lack of Republican voter support for the war in Afghanistan,” said Republican strategist Mike Murphy. “I think we have hit a tipping point politically and this will emerge as a very big story in the Republican primaries later this year.”

Indeed, polling suggests that Republican voters would be receptive to a skeptical message. For the first time in Washington Post-ABC News polling, more people disapprove of Obama’s handling of the war than support it. And the biggest shift is among Republicans, who've grown increasingly critical of the president's performance on the issue. In January, 41 percent said they supported Obama’s approach to the war. Now only 23 percent do. Only half of Republicans still think the war is worth fighting. (In May of 2010, 69 percent of Republicans thought the war was worth fighting.)

There are a few other signs of a shift. In 2010, when former Republican National Committee chairman Michael Steele somewhat clumsily called the war “one of Obama’s choosing,” and "not something the U.S. had actively prosecuted or wanted to engage in," he was roundly condemned by conservatives. While some neoconservative pundits criticized Barbour, saying he was “pandering,” the backlash was not nearly as strong. Rep. Jason Chaffetz (R-Utah), a likely Senate candidate in 2012, has criticized the war and opposed sending more troops, a position that Republican strategists there say has not hurt him with voters.

It’s not clear who could take up Barbour’s mantle. So far, the only other candidates to question U.S. war involvement are the libertarian-minded long-shots — former New Mexico governor Gary Johnson and Texas Rep. Ron Paul. Former Minnesota governor Tim Pawlenty has gone the opposite route, praising the war effort and opposing defense spending cuts. Former Massachusetts governor Mitt Romney has made similar comments, criticizing Obama’s leadership but not the war itself. (He also recently described the current situation as “peacetime,” suggesting war policy is not a major focus for his campaign.) Former House Speaker Newt Gingrich has predicted that the war is “not going to end well,” but he wants to extend our commitment, not cut it short.

“The real question is, is there a candidate in the race who has the same chutzpah [as Barbour], who isn’t afraid to take that position,” said Brian Donahue, a Republican strategist. As Republican voters’ opinions change, he said, “It would benefit candidates running for president to stake out a thoughtful position, even if that position doesn’t look exactly like what former President Bush’s position was.”

Should Indiana Gov. Mitch Daniels enter the race, he would be the logical standard-bearer for Barbour’s cause. Like his good friend in Mississippi, Daniels has suggested defense spending cuts. But it’s not clear that Daniels is planning to run. There’s also former Arkansas governor Mike Huckabee, who recently said he saw no “endgame” in Afghanistan. But he too has given mixed signals about his desire to get in the race. Once the debates begin and the field narrows, we’ll see who — if anyone — will take up the issue of this nearly decade-old war.