By Steven R. Hurst, Associated Press

WASHINGTON — Supporters of Democratic presidential candidate Barack Obama heaped criticism on Republican opponent John McCain for saying it was "not too important" when American troops are withdrawn from Iraq, as Democrats leapt at the chance to attack the Arizona senator's position on the unpopular war.

But Obama also took a public relations hit Wednesday when Jim Johnson, a manager of the Illinois senator's vice presidential search team, resigned under criticism over his personal loan deals.

In the third day of their one-on-one bid for the White House — after Democrat Hillary Rodham Clinton dropped out of the race — both Obama and McCain appeared somewhat off balance as their campaign message machines were gummed up by distractions.

McCain has been a supporter of the Iraq war, particularly last year's decision by the White House to boost troop strength to bring down raging violence. He was critical of the early management of the war, but strongly supported last year's troop build up, now being reversed, and says it was successful.

Obama has opposed the war from the outset and promises to bring American troops home within 16 months of taking office.

Their differences got a fresh airing when McCain was asked on NBC television — given the drop in Iraqi violence — if he had a better estimate for when American forces could leave the country.

"No, but that's not too important," McCain said. "What's important is casualties in Iraq.

"Americans are in South Korea. Americans are in Japan. American troops are in Germany. That's all fine. American casualties, and the ability to withdraw. We will be able to withdraw. ... But the key to it is we don't want any more Americans in harm's way."