Putin told television station RT that policies embraced by U.S. President Barack Obama were under threat from a "conservative" opposition in the country.
"My feeling is that he is a sincere man and that he sincerely wants to implement positive change," Putin said. "But can he do it ... will they let him do it?"
The governments are at odds over U.S. plans to deploy a missile defense shield in Eastern Europe.
The Democratic National Platform laid out Obama's plans for missile defense. While the United States and Russia can cooperate on issues like missile defense, the administration has made it clear it would move forward with its own system in Eastern Europe.
Putin said that, while he could work with Republican presidential nominee and former Massachusetts Gov. Mitt Romney, he was concerned about any policy shifts under a Romney administration.
"When we talk about the missile defense system, our American partners keep telling us, 'This is not directed against you,'" said Putin. "But what happens if Mr. Romney, who believes us to be America's No. 1 foe, is elected as president of the United States?"
Romney during a campaign event last month described Russia as the "No. 1 geopolitical foe" of the United States.