Sen. John McCain, R-Ariz., says a full troop withdrawal in Afghanistan would be a mistake.
McCain, the top Republican on the Senate Armed Services Committee, thinks the war effort would benefit from one more season of fighting.
"I would be very reluctant to reduce the surge troops capabilities, support troops," he said. "I agree with Secretary Gates who has strongly stated that a modest withdrawal is important. This date never should have been set to start with it was done for political reasons with no recommendation from any of our military leaders."
On a trip to Afghanistan earlier this month, retiring Defense Secretary Robert Gates advocated for a comprehensive decision from the president on the Afghan war strategy.
"I think to make a decision on July in complete isolation from anything else has no strategic meaning," he said. "And so part of that has to be kind of, what's the book end? Where are we headed? What's the ramp look like?"
Gates retirement from the Pentagon becomes official on June 30.
Military commanders want to keep U.S. forces in Afghanistan for as long as possible, arguing that too fast a withdrawal could undermine the fragile security gains in the fight against the Taliban.
There is also growing political pressure on Capitol Hill for a more significant withdrawal. Twenty-seven senators, Democrats as well as Republicans, sent Obama a letter last week pressing for a shift in Afghanistan strategy and major troop cuts.
"Given our successes, it is the right moment to initiate a sizable and sustained reduction in forces, with the goal of steadily redeploying all regular combat troops," the senators wrote. "The costs of prolonging the war far outweigh the benefits."
President Obama has said he favors a significant withdrawal.
At a democratic fundraiser in Washington Monday night, Obama said that by the end of the year, "We will be transitioning in Afghanistan to turn over more and more security to the Afghan people."
There is broad public support for starting to withdraw U.S. troops.
According to an Associated Press-GfK poll last month, 80 percent of Americans say they approve of Obama's decision to begin withdrawal of combat troops in July and end U.S. combat operations in Afghanistan by 2014. Just 15 percent disapprove.