Gen. David Petraeus will take the next step in replacing Gen. Stanley McChrystal to lead the war in Afghanistan on Tuesday.
He is scheduled to testify before the Senate Armed Services Committee on the mission to defeat the Taliban and restore relations with civilian leaders.
McChrystal was fired last week by President Barack Obama after he and his aides criticized the administration in an article for Rolling Stone Magazine.
"This is a chance to start over completely," said Sen. Lindsey Graham, a South Carolina Republican who is influential on military issues.
Graham said he would be "very concerned if nothing changes on the civilian side" because the civilian-military relationship has grown "dysfunctional."
"On the Democratic side, there is solid support. But there's also the beginnings of fraying of that support" for the war, said Sen. Carl Levin, D-Mich., chairman of the Armed Services Committee.
No major changes in war strategy are expected, because McChrystal based his strategy largely on Petraeus' ideas. He is expected to be confirmed as early as this week.