Two key Barack Obama advisers seemed to differ Tuesday on how willing the presumptive Democratic nominee would be to tweak his plan to withdraw troops from Iraq.

The Illinois senator has said he wants to begin removing one to two combat brigades per month immediately after becoming president, and have all brigades out of the country within 16 months.

But Missouri Sen. Claire McCaskill, a campaign co-chair, and Susan Rice, a foreign policy adviser, were both asked Tuesday whether Obama would consider changing course, given a report in The New Yorker that suggested he would. The article said Obama's original plan "could revive the badly wounded Al Qaeda in Iraq, re-energize the Sunni insurgency ... and return the central government to a state of collapse."

In an interview with MSNBC, Rice said Obama has been "consistent" on the matter, but that the 16-month plan is just an estimate -- she suggested Obama has left himself wiggle room.

"That's not a deadline. That's a timetable," she said. "And, obviously, as Senator Obama has said on numerous occasions, he will listen to his commanders on the ground; he will follow and heed their advice, as he decides how at the strategic level we must proceed."

McCaskill, asked the same question on the same network, was unequivocal.

"Well, first, no. No, he will not (change course). And Senator Obama fundamentally disagrees with that assessment," she said. "If you can't leave Iraq when it's stable and you can't leave when it's not stable, that means that we are stuck with George Bush and John McCain; we can never leave Iraq.

"... It is unsustainable to continue to prop up, in the middle of a civil war, an Iraqi government that will not step up and do what they need to do to take over for their country. Now is the time that we need to carefully and reasonably withdraw," she said.

Republicans criticized both advisers for their respective statements.

The Republican National Committee sent around an e-mail calling Rice's statement a preview of "Obama's coming reversal on immediate withdrawal from Iraq."

John McCain's campaign then released a statement saying McCaskill's comments make Obama's coming trip to Iraq ring hollow.

"The American people deserve a leader who will make decisions based not on ideology but on what most serves our national interests and in consultation with our commanders on the ground," the campaign said. "If Obama is resolved to maintain his reckless commitment to immediate withdraw from Iraq just as our troops are on the cusp of victory, then his planned trip to the front will be nothing more than a photo-op, and a distraction to the brave men and women who are fighting and winning the war there."