More troops may be needed in Afghanistan, Sen. John McCainJohn Sidney McCainMeghan McCain: Harris 'sounded like a moron' discussing immigration Arizona AG Mark Brnovich launches Senate challenge to Mark Kelly Arizona Democrats launch voter outreach effort ahead of key Senate race MORE (R-Ariz.) suggested Thursday.

McCain, the top Republican on the Senate Armed Services Committee, said that it may be necessary to increase troop levels as other countries default on their commitments to send forces into Afghanistan.

"I believe so, particularly since our allies that we had counted on for supplying some 10,000 troops clearly are not going to do that," McCain said when asked if more troops were needed during an appearance on ABC's "Good Morning America."

President Barack ObamaBarack Hussein ObamaEnding the same-sex marriage wars Arizona election audit draws Republican tourists Biden tries to erase Trump's 'America First' on world stage MORE had already orchestrated a "surge" of troops in Afghanistan that infused some 30,000 troops into Afghanistan this year to help quash a mounting insurgency. Republicans like McCain had clamored for this surge, but have been sharply critical of a timeline within that strategy that looks to begin withdrawing troops in July of 2011.

McCain was critical of the idea of a timeline, as many Republicans have been, warning instead that "it's all about conditions on the ground."

McCain and other Republicans fear that communicating a firm withdrawal strategy could encourage enemy forces to simply wait out the U.S. in Afghanistan.

Obama found a new general on Wednesday, David Petraeus, to lead U.S. efforts in Afghanistan. The president installed Petraeus, the guru of the Iraq counterinsurgency, in that role after accepting the resignation of Gen. Stanley McChrystal, who made controversial remarks to Rolling Stone magazine.