WASHINGTON (CNN) -- A leading Democratic congressman Wednesday challenged the top U.S. general in Iraq to explain why the United States should keep large numbers of troops in that country.
Gen. David Petraeus and Ambassador Ryan Crocker testify before the House Armed Services Committee Wednesday.
"We and the American people must ask: Why should we stay in Iraq in large numbers?" Rep. Ike Skelton, the chairman of the House Armed Services Committee, demanded as Gen. David Petraeus began testifying.
"I hope you can also explain the next strategy," Skelton asked asked. "The counterinsurgency strategy worked tactically, but the surge forces are going home. Political reconciliation hasn't happened, and violence has leveled off and may be creeping back."
"So how can we encourage and not force the intransigent political leaders of Iraq to forge a real nation out of the base sectarian instincts? So what is the new strategy?" the Missouri Democrat asked.
Wednesday was day two of Petraeus and Crocker testimony on Capitol Hill. On Tuesday , the two spent about nine hours giving the Senate Armed Services and Foreign Relations committees their assessments of the 5-year-old war.
Petraeus said in the seven months since their last appearance before Congress, U.S. and Iraqi forces have made progress toward tamping down the violence, but progress was "fragile" and "reversible." Watch Petraeus call the progress "significant" but "uneven" »
Petraeus also recommended that troop withdrawals from Iraq be paused for 45 days after July when the U.S. in Iraq will be reduced to 140,000.
Asked whether further troop reductions could resume after the pause, Petraeus repeated his position that future troop levels be based on conditions on the ground.
"This approach does not allow establishment of a set withdrawal timetable," he said on Tuesday. "However it does provide the flexibility those of us on the ground need to preserve the still-fragile security gains our troopers have fought so far and sacrifice so much to achieve." Watch Petraeus tell representatives what the U.S. is fighting for »
Democratic senators, as well as some Republicans, expressed frustration that an end to the Iraq deployment did not appear to be in sight.
"War is not a linear phenomenon," Petraeus said. "It's a calculus, not arithmetic."
That answer was not good enough for Democratic senators. Sen. Joseph Biden, the Foreign Relations Committee's chairman, said continued U.S. involvement was "unsustainable."
"We have gone from drowning to treading water," said Biden, D-Delaware, who mounted an unsuccessful presidential campaign earlier this year. "We are still spending $3 billion every week and we are still losing ... 30 to 40 American lives every month. We can't keep treading water without exhausting ourselves, and that is what the president seems to be asking us to do." Watch Biden call Petraeus "straightforward and honest" »
However, Sen. John McCain, the top Republican on the Armed Services Committee and the presumptive GOP presidential nominee, said because of last year's troop increase, the United States is no longer "staring into the abyss of defeat." Watch McCain call Iraq a "hard road" »
"Success, the establishment of peaceful, democratic state, the defeat of terrorism -- this success is within reach," he said. "Congress must not choose to lose in Iraq. We must choose to succeed." E-mail to a friend