The unsteady center of the Iraq debate shifted when Republican maverick Chuck Hagel, a decorated Vietnam veteran, joined Senate Democrats in backing a troop-withdrawal timeline.

With his vote on the $123 billion war supplemental (HR 1591) on March 29, which included the timeline, Hagel became one of four Senate Republicans to buck the White House more than once on Iraq policy during this young Congress.

Those four mavericks — Hagel, Gordon H. Smith of Oregon, Susan Collins of Maine and Norm Coleman of Minnesota — are up for re-election in 2008, and Hagel is still considering a presidential bid.

A total of 21 Senate seats now held by Republicans will be up in the 2008 election. But the GOP held the votes of far more of those members than it lost — both on the supplemental and on an earlier Iraq policy barometer, a Feb. 17 vote to end debate on a motion to proceed to a bill expressing disapproval of President Bush’s Iraq troop surge (S 574).

At least one Republican senator with a seat to defend — Lindsey Graham of South Carolina — says there is no chance that his position on leaving Iraq will change, even if it means losing his seat.

Others, though, have not made such clear declarations, and they may not have to this far from the 2008 election.

“There are a lot of votes between now and then,” said Linda Fowler, a political science professor at Dartmouth College in New Hampshire, where Republican Sen. John E. Sununu will be defending a seat next year. “It may very well be that the acid test for the Republican senators in New England really won’t come until this summer.”

Smith, who announced his opposition to the war last December, said he has talked to Republican senators, both those who face re-election in 2008 and those who don’t, who share his concerns about Iraq.

“I’m not going to out them, but I am not alone,” he said.

Like Fowler, Smith predicts that lawmakers will have a clearer view of the conflict and the efficacy of Bush’s troop surge by August.

For now, most Republicans — including Coleman, Collins and Sununu, all of whom voted against the supplemental — remain steadfastly opposed to writing a timetable for withdrawal into law.

“I just think it’s bad policy to tell the enemy, ‘This is when we’re leaving,’ ” Coleman said after voting to strip the withdrawal language from the supplemental.

Politically, Coleman and other Republicans risk alienating their base if they move too precipitously away from the president. But if voters want a change of Iraq policy, remaining in league with Bush could hurt their re-election hopes, said University of Minnesota political science professor Larry Jacobs.

“The main challenge that Norm Coleman has is that his position on Iraq has to keep the loyalty and enthusiasm of Republican voters while reaching out to independent voters,” Jacobs said.

The hope within the Republican Party is that the recent troop surge quells violence in Iraq and leads to a stabilization.

That would enable U.S. forces to hand control to the Iraqi government. A peaceful transfer of power over a stable country, in turn, should benefit Republican candidates in 2008, they say.

“The Iraq policy right now is the right policy, and I think it will make for good politics,” said Sen. Mel Martinez, R-Fla., who is chairman of the Republican National Committee.

Martinez, who is not up for re-election in 2008, said, “Democrats are overreaching” on the politics of the war.

While Democrats push their GOP colleagues to defect from the president’s position on Iraq, it’s not clear even to political experts that doing so at this point would yield any benefit on Nov. 4, 2008.

“I don’t know necessarily that the voters reward early independence as opposed to later independence,” Fowler said.

For Graham, there is no such thing as deciding when to split from Bush on Iraq. He unequivocally states that he will not. “I’m willing to lose my job over this,” he said.

Graham, however, is far more vulnerable to a GOP primary challenge than to a Democratic opponent in heavily Republican South Carolina.

Political scientists say Republican senators in swing states have room to oppose troop withdrawals at this point in the election cycle because they are not getting hammered by anti-war challengers; the president’s looming veto threat puts the war more squarely on his shoulders; and, in some cases, their home-state colleagues are voting the same way.

Sununu has been more critical of the Iraq War than the senior senator from New Hampshire, fellow Republican Judd Gregg. And he has found other issues, including the Patriot Act (PL 107-56) and the job status of Attorney General Alberto R. Gonzales, on which to differentiate himself from the president.

Breaking from Bush on the war could cost him, particularly if the troop surge is successful, Fowler said.

“If I were Sununu I would sort of say, ‘I’m going to hold my fire for a while and it may not be prudent to break too early with the president,’ ” Fowler speculated.

Coleman said he believes public opinion is having an effect on the Iraq debate, but, “You certainly don’t fight a war based on polls.”

Jacobs said Coleman “can kind of troll along here, tread water. The more time he does that, the more time he gives the new policy in Iraq to take effect.”

Casting votes on the war is not necessarily an easy call for Democrats, either, as they balance sentiment for ending it against a need to avoid being seen as undermining the U.S. effort.

Sen. Mark Pryor, D-Ark., who will try to defend his seat for the first time next year, voted with nearly all Republicans to strike the withdrawal provision from the war spending bill.

Of the six Democrats not ranked “safe” for re-election by CQ, Pryor was the only one to oppose the withdrawal timeline.

Sen. Mary L. Landrieu of Louisiana, whose race CQ rates as “leans Democratic,” and Sens. Tom Harkin of Iowa, Max Baucus of Montana and Frank R. Lautenberg of New Jersey, all of whom are ranked “Democrat favored,” voted to keep the withdrawal provision.

The most politically vulnerable Democrat, Tim Johnson of South Dakota, did not vote because he is recovering from a brain hemorrhage.