Clinton has slipped three points among Democrats and seven points among independents since January. Among Republicans, she slipped a full 10 percentage points.
The poll also looked at Sen. Marco Rubio (R-Fla.), who, along with Clinton, many political watchers believe could seek the White House in 2016.
Unlike Clinton and Obama, Rubio's favorability numbers have remained steady through the recent Senate debate on comprehensive immigration reform. But that could be largely because Rubio remains unknown to much of the country.
According to the survey, 26 percent of those polled had a favorable opinion of Rubio while a quarter of Americans had an unfavorable opinion. Some 49 percent said they had no opinion of the Florida lawmaker. That's down just marginally from last August, when 29 percent had a favorable view, 26 percent had an unfavorable one, and 45 percent said they didn't know.
The survey of 1,010 adults carried a margin of error of plus or minus 3.5 percentage points.