On Capitol Hill, seniority rules - Obama and Clinton take a back seat to second-tier candidates during Senate hearings.

Seizing a chance to deliver his critique of the war, the Illinois senator left himself only a few minutes to ask questions of the commander of all U.S. ground forces in Iraq and the U.S. ambassador to Baghdad.

And he got no sympathy from Sen. Joseph R. Biden Jr. of Delaware -- the chairman of the Senate Foreign Relations Committee and, as it happens, a rival for the Democratic nomination. Obama noted that he had "very little time to ask questions, and that's unfortunate."

Biden broke in: "That's true, Senator."

Far and away the biggest spectacle on Capitol Hill this week was the report on the Iraq war from Army Gen. David H. Petraeus and Ambassador Ryan Crocker. They appeared before two House committees on Monday and two Senate panels Tuesday, telling lawmakers that leaving the battlefield now would be a mistake.

But the 2008 campaign was also front and center: Of the 10 members of Congress who are running for president, six were behind the microphones, asking questions.

The hearings were a chance for them to reach a national audience without dipping into limited advertising budgets. They were also something of an equalizer; Obama's charisma and Sen. Hillary Rodham Clinton's celebrity might soak up all the attention in Iowa and New Hampshire, but on Capitol Hill, seniority rules.

As a comparatively junior member of the armed services committee, Clinton didn't get to speak until several hours into Tuesday's hearing. Iraq has proved a sensitive issue for her campaign. She voted in 2002 to authorize the use of U.S. military force in Iraq but now is calling for troops to be withdrawn.

When she addressed the general, her focus was not her own evolution on Iraq, but what she saw as a "contradiction" in his testimony.

She noted that in the morning, he had told Biden that if conditions in Iraq were unchanged in a year, he would be hard-pressed to recommend keeping up to 160,000 troops deployed. Yet when he was asked a similar question in the afternoon, he said he would have to consider what to do, Clinton said.

"General, don't you think the American people deserve a very specific answer about what is expected from our country?" she asked.