The most recent Pew Forum study found that support for abortion among the American public has declined.

Polls conducted in 2009 have found fewer Americans expressing support for abortion than in previous years. In Pew Research Center polls in 2007 and 2008, supporters of legal abortion clearly outnumbered opponents; now Americans are evenly divided on the question, and there have been modest increases in the numbers who favor reducing abortions or making them harder to obtain. Less support for abortion is evident among most demographic and political groups.
. . .
No single reason for the shift in opinions is apparent, but the pattern of changes suggests that the election of a pro-choice Democrat for president may be a contributing factor.

Read the entire article, which includes graphs.