WASHINGTON – In the past two weeks, three prominent Republican senators have defected on Iraq. One, Sen. George V. Voinovich of Ohio, even wrote President Bush a letter to explain the reasons for his reversal.

Sen. Olympia J. Snowe of Maine, a GOP moderate from one of the most anti-war states in the country, hasn’t reached for pen and paper, but she’s close. Like Voinovich and Republican Sens. Pete V. Domenici, N.M., and Richard G. Lugar, Ind., Snowe believes that the current U.S. policy toward Iraq is broken and that Bush must change direction. She’s just waiting for the right alternative to come to a vote.

Her voting struggles over Iraq started in February. Snowe had to decide between supporting Republican efforts to block a Democratic statement of opposition to Bush’s troop buildup in Iraq or voting to allow the resolution to go forward, using the opportunity to articulate her own growing concerns about the war.

She was a loyal Republican in that debate. But within days, Snowe regretted her decision and later broke with the GOP to demand another chance to oppose the troop increase.

All this bared the internal debate of one of the Senate’s most conflicted members. Although Snowe insists that she has had it with the war, as late as March she voted against setting deadlines on when the troops should come home. Over 24 years in Congress, she said, she has never felt such anguish. “These are life-and-death challenges in an intractable war,” she said. “It’s American blood.”

Come September, perhaps no other Republican senator will be closer to bolting from the president’s position if Gen. David H. Petraeus’ much-anticipated assessment comes up short.

Moment of truth: Snowe made her first trip to Iraq in March 2006, as the government in Baghdad struggled to select a prime minister and a Cabinet – and the Bush administration, she said, sat on the sidelines. “The administration should have been driving the agenda to make sure the Iraqis were making the political decisions to form their government,” she said. “The danger was indisputable.”

Latest visit to Iraq: May 2007. “It was infinitely worse, in spite of the surge and the additional troops,” she said. “I’ve been to war zones. You know when it’s working and when it isn’t, and really, it was an ironclad shutdown.”

Outlook: Petraeus must show more than progress. He needs to show victory. “Those benchmarks have to be met. That’s it,” Snowe said without equivocation. “Enough is enough.”

Most persuasive argument from war supporters: “People say if we pull out, it could get much worse. There could be a real bloodbath.”