The Republican Party has moved to the far right in recent years–far to the right of Barry Goldwater and even Ronald Reagan–while the Democrats have moved towards the middle. The voteview blog has analyzed recent presidents and the result is exactly what we already knew:
Our findings here echo those discussed in a prior post that Republicans have moved further to the right than Democrats to the left in the contemporary period. Indeed, as seen below, President Obama is the most moderate Democratic president since the end of World War II, while President George W. Bush was the most conservative president in the post-war era.
On the other hand, in many ways Obama has had success at passing liberal polices in some areas where other Democratic presidents have failed. This success might be partially because of his moderation, and that a more liberal Democrat might have had fewer successes.