Senator Barack Obama has rushed to clarify his position on the Iraq War after he appeared to wobble on a commitment to withdraw US ground troops within 16 months, a central plank of his candidacy.
The Democratic presidential nominee used a press conference to say that the timetable was not set in stone and that he would adjust his plans based on conditions on the ground when he visits Iraq later this month.
On his website, Mr Obama promises he "will remove one to two combat brigades each month, and have all of our combat brigades out of Iraq within 16 months".
But he told journalists in North Dakota that those policies could be "refined" in the light of what he finds in Iraq.
"I've always said the pace of withdrawal would be dictated by the safety and security of our troops and the need to maintain stability," he said.
"When I go to Iraq and have a chance to talk to some of the commanders on the ground, I'm sure I'll have more information and will continue to refine my policies."
Brian Rogers, a spokesman for Mr McCain, said: "Since announcing his campaign in 2007, the central premise of Barack Obama's candidacy was his commitment to begin withdrawing American troops from Iraq immediately. Today, Barack Obama reversed that position proving once again that his words do not matter.
"Now that Barack Obama has changed course and proven his past positions to be just empty words, we would like to congratulate him for accepting John McCain's principled stand on this critical national security issue.
"If he had visited Iraq sooner or actually had a one-on-one meeting with General (David) Petraeus, he would have changed his position long ago."
The charge stung Mr Obama into a swift response. He held a second press conference just a few hours later to clarify his comments.
He accused the McCain camp of suggesting "we were changing our policy when we haven't".
"I've given no indication of a change in policy. I intend to end this war. That position has not changed. I have not equivocated on that position. I am not searching for manoeuvering room with respect to that position," Mr Obama said.
The charge that he is changing his mind is toxic for three reasons.
It allows Mr McCain to argue that he, not Mr Obama, has a better understanding of what now needs to be done in Iraq.
Secondly, it gives Republicans evidence to use to depict Mr Obama as just another cynical politician prepared to change his position to win votes.
Finally, any shift on Iraq risks alienating the left-wing of his own party, who have grown uneasy at some more moderate positions he has struck in recent weeks.
© Copyright of Telegraph Media Group Limited 2008.