The three presidential aspirants and Senators took turns grilling Army Gen. David Petraeus and U.S. Ambassador to Iraq Ryan Crocker on Tuesday.

Sen. John McCain (Ariz.), the presumptive GOP presidential nominee, held the advantage in speaking order; as the ranking member on the Senate Armed Services Committee, McCain spoke early in the day and used his platform to praise Petraeus and progress in Iraq.

Dueling Democratic presidential candidates Sens. Hillary Rodham Clinton (N.Y.), an Armed Services member, and Barack Obama (Ill.), who holds a slot on the Foreign Relations Committee, asked Petraeus some tough questions, but Obama in particular — the last of the candidates to speak at the end of two hearings — seemed to be thinking about the campaign trail.

“I continue to believe that the original decision to go into Iraq was a massive strategic blunder that the two problems 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 said in a closing statement.

“That’s not a decision you gentlemen made. I won’t lay it at your feet. You are cleaning up the mess afterwards,” he added. “But I think it is important as we debate this forward.”

Petraeus and Crocker started the day at the Armed Services Committee.

In his six-minute opening statement, McCain praised the success of the troop surge that he has ceaselessly talked up on the campaign trail. Although work in Iraq is unfinished, McCain argued that success was now possible.

“Much, much more needs to be done,” McCain stressed. “But today, it is possible to talk with real hope and optimism about the future of Iraq and the outcome of our efforts there.

“We’re no longer staring into the abyss of defeat, and we can now look ahead to the genuine prospect of success,” the former Vietnam veteran and prisoner of war stated.

McCain urged Congress to give the military and political team in Iraq time to finish their business. “We have before us a hard road,” McCain said. But, he added, “the alternative path is in the end the far costlier.”

“Congress must not choose to lose in Iraq. We must choose instead to succeed.”

Both McCain and Sen. Carl Levin (D-Mich.) questioned Petraeus about what and when he knew about last weekend’s Basra offensive led by Iraqi Prime Minister Nuri al-Maliki. Not much, Petraeus confirmed.

Meanwhile, Clinton, doing her best to sound wonky and measured, criticized the lack of political progress on the ground in Iraq and the “opportunity costs” in terms of lost military resources in other global hot spots of an open-ended commitment in Iraq.

“I think it’s time to begin an orderly process of withdrawing our troops,” Clinton stated, echoing what she has said on the campaign trail.

Clinton then pointedly asked Petraeus to clarify what conditions would have to be present in order to withdraw from Iraq.

“What conditions would have to exist for you to recommend to the president that the current strategy is not working?” Clinton queried.

Petraeus responded that there was no “mathematical equation.”