President Barack Obama stressed Sunday evening that the United States is going “to provide assistance to Afghanistan for a long time to come” as he sought to end the “obsession” over when the U.S. military will withdraw from the nation.

“My focus right now is how do we make sure that what we’re doing there is successful,” he said in response to reporters’ questions at a news conference at the Group of 20 meeting in Toronto. He added, “I’ve signaled very clearly that we’re not going to just keep on doing things if they’re not working, and that by next year we will begin a process of transition.”

The president laid out his plan in December for the war in Afghanistan. It incorporated a surge of troops, like the strategy used in Iraq, that will reach its peak this fall, followed by the beginning of a withdrawal in July 2011.

Republicans have criticized Obama for announcing an end date and have called on him to consider conditions on the ground before beginning a withdrawal. Senate Armed Services ranking member John McCain said Sunday morning, “We have to convince the enemy that we are going to do what’s necessary to succeed.” The Arizona Republican spoke on NBC’s “Meet the Press.”

At the G-20 news conference, Obama emphasized the review process. “What I expect is that by the end of this year, we will have seen progress on the strategy that was laid out,” he said. “We will conduct a full review. Those things that are not working, we will fix.”