Story Highlights • Two notable Republican senators ask President Bush to change course on Iraq

• Analysts say prominent senators' opinions could sway others

• CNN/Opinion Research poll shows GOP support for war at all-time low

• Observers say to expect more defections as Iraq report, elections near

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WASHINGTON (CNN) -- With the election season and a key Iraq war progress report perched on the horizon, more Republicans will start to distance themselves from President Bush's Iraq policy, analysts say.

Two respected senior GOP senators this week publicly asked the president to look for a way out of Iraq. One of them -- Sen. Richard Lugar of Indiana -- is the top Republican on the Senate Foreign Relations Committee.

"When Dick Lugar comes out against your foreign policy, it means your dam is breaking, and it means we're far more likely as a country to move from Plan A to Plan B this fall, when it comes to Iraq," said David Gergen, who has advised both Republican and Democratic presidents. (Watch why Lugar has broken with the president on Iraq )

Sen. George Voinovich, R-Ohio, is jumping straight to what he calls Plan "E" for "Exit."

"It's time for the United States to put together a comprehensive plan for gradual disengagement in Iraq," Voinovich said. "We're running out of time and I don't think it's fair to the next administration to say, 'Hey by the way, we're leaving this baby for you guys to figure out.' "

In a letter to the president, Voinovich, also a member of the Foreign Relations Committee, called for military disengagement and increased diplomatic engagement.

Both Lugar and Voinovich said they don't favor setting timetables for withdrawing U.S. troops from Iraq but they are trying to get Bush's attention and convince him that it's time to develop an exit strategy.

In fact, in the position paper Voinovich sent to Bush, called "The Way Forward in Iraq," he cited the possibility that voters might elect a president in 2008 who would promise an immediate withdrawal from Iraq as a reason to change course. (Watch why the defections may spell the end of Republican support )

Voinovich said there are more Republicans who feel the same.

"I think many of my colleagues share my concerns," he said. "They're frustrated."

Some, however, still support the policy.

When asked about Lugar's remarks, Sen. Lindsey Graham, R-South Carolina, said, "As much as I respect Sen. Lugar, I think it's unfair to the troops in the field to say the surge is not working."

"The military part of the surge is definitely working," Graham said. "There's no question in my mind that there's improvement in stability and new political alliances being formed."

The top U.S. commander in Iraq, Gen. David Petraeus, and the U.S. ambassador, Ryan Crocker, are to issue a report in September on what impact Bush's surge of troops into the war is having. Analysts say that report will be pivotal on both the country's and Congress' outlook on the war.

Lugar's and Voinovich's reversal on Iraq are the most significant of a growing number of Republicans who are beginning to distance themselves from Bush's strategy for Iraq. And with voters becoming increasingly against the war, look for more to follow, analysts say.

A CNN/Opinion Research Corp. poll released Tuesday shows that 38 percent of respondents who identified themselves as Republicans say they oppose the war.

That follows a trickle of Republican lawmakers making their displeasure with Bush's Iraq policy public.

Earlier in June, several Republican members of Congress called for the Bush administration to follow the recommendations made by the bipartisan Iraq Study Group, which Bush had resisted to follow.

This week, Republican congressmen Christopher Shays of Connecticut and Frank Wolf of Virginia are calling to reconvene the ISG to review Iraq policy and offer new recommendations.

"Last fall, the Iraq Study Group provided Congress a thoughtful assessment on one of the most important issues of our time," Shays said. "As we approach another crossroad in this conflict, having that thoughtful insight again will be invaluable."

A number of Republicans endorsed the amendment, which was passed by the House 355-69.

Analysts and Republican strategists say it's one thing for a few lesser-known Republicans to go against the White House; but some believe a respected senior party stalwart like Lugar turning against the war gives cover for other skeptical Republicans of Lugar's stature, like Sen. John Warner of Virginia, to make a break from the administration's position.

Warner, the ranking Republican on the Senate Armed Services Committee, hinted that might be coming.

"I have some thoughts of my own but I will withhold those thoughts until I participate in the debates over the (Defense Authorization Bill) after the Fourth of July."

Analysts say a different surge might be in the offing as September nears -- a Republican surge for withdrawal.

"I think we will certainly see other Republicans following the Lugar lead," said Stuart Rothenberg of the Rothenberg Political Report. "Most or all of them will wait closer until September, when we get the report from General Petraeus, and when Congress as a whole and in fact the White House will be re-evaluating the policy."

CNN's Dana Bash, Brian Todd and Ted Barrett contributed to this report.