Petraeus faces presidential hopefuls

"I think it's time to begin an orderly process of withdrawing our troops, start rebuilding our military and focusing on the challenges posed by Afghanistan, the global terrorist groups and other problems that confront America," she said.

She pressed Petraeus on what conditions would have to exist for him to recommend to the president that the current strategy is not working. He responded that the factors include the status of the enemy, Iraqi forces, local governance and the economic and political situations, but "it's not a mathematical exercise."

Clinton also objected to Crocker's statement that the Iraqi parliament will get a chance to review a U.S.-Iraqi agreement that would give legal authority for American troops to remain in Iraq, but Congress will not. "It seems odd," she said, adding that she has legislation that would require congressional review.

Clinton said Iraq presents a "very difficult dilemma" for decision-makers. "If this were easy or if there were a very clear way forward, we could all perhaps agree on the facts about how to build toward a resolution.

Obama: Start bringing troops home
Obama pressed Petraeus and Crocker on their standard for success in Iraq. The Illinois senator and Democratic front-runner said he worries that the goals — completely eliminating al-Qaida and Iranian influences — may be impossible to achieve and troops could be there for 20 or 30 years in a fruitless effort.

"If, on the other hand, our criteria is a messy, sloppy status quo but there's not huge outbreaks of violence, there's still corruption, but the country is struggling along, but it's not a threat to its neighbors and it's not an al-Qaida base, that seems to me an achievable goal within a measurable timeframe," he said.

Obama said Bush's troop increase reduce the violence, but the "breathing room" it created has not been used effectively as rivals jockey for political power in Basra. Obama argued that the best way to resolve the political situation is by withdrawing troops in a measured way that increases pressure on both sides.

He also said any future steps should include U.S. diplomatic engagement with Iran. "I do not believe we're going to be able to stabilize the position without them," he said.

Invasion Iraq: Gen. Petraeus testimony U.S. data shows 'surge' effect See charts accompanying Gen. Petraeus’ testimony to Congress regarding U.S. military progress in Iraq.

"I continue to believe that the original decision to go into Iraq was a massive strategic blunder (and) that the two problems (of withdrawing troops) that you've pointed out — al-Qaida in Iraq and increased Iranian influence in the region — are a direct result of that original decision," Obama told Petraeus and Crocker.

Obama opposed the war while rivals Clinton and McCain voted in 2002 to authorize the use of military force in Iraq.

Obama received some senatorial courtesy from Sen. Bill Nelson, D-Fla., even though he's a Clinton backer. Nelson should have gone before Obama in the questioning, but three hours into the hearing he let Obama go ahead so he could avoid a scheduling problem. Obama had two campaign fundraisers to attend.

Earlier in the day, Obama criticized McCain on NBC's TODAY show. "John McCain has not offered any clear point at which he suggests it's time for us to move our troops home," Obama said.

Picking the president: The candidates Click to visit that candidate's MSNBC page or click the XML symbol for an RSS feed. John McCain                Barack Obama

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