FARGO, N.D. – Democrat Barack Obama struggled Thursday to explain how his upcoming trip to Iraq might refine, but not basically alter, his promise to quickly remove U.S. combat troops from the war.

A dustup over war policy – one of the main issues separating the Illinois senator from his Republican opponent, John McCain – overshadowed Mr. Obama's town-hall meeting here with veterans.

Republicans said Mr. Obama was altering one of the core policies that drove his candidacy "for the sake of political expedience." He denied, with equal intensity, that he was shifting positions.

"I am going to do a thorough assessment when I'm there," he said of his trip to Iraq. "I'm sure I'll have more information and continue to refine my policy."

He left the impression that his talks with military commanders there could change his promise to remove U.S. combat troops within 16 months of taking office.

Hours later, he sought to clarify his statement, and he accused Mr. McCain's campaign of suggesting a policy change where none had occurred.

"I have said throughout this campaign that this war was ill-conceived, that it was a strategic blunder and that it needs to come to an end," Mr. Obama said. "I have also said I would be deliberate and careful about how we get out. That position has not changed."

He promised to summon the Joint Chiefs of Staff on his first day in office "and I will give them a new mission and that is to end this war, responsibly and deliberately, but decisively." The Associated Press