Former Secretary of State Hillary Clinton remains the 2016 presidential candidate to beat, but her handling of the Benghazi, Libya assassination of the U.S. ambassador, panned by the public, has significantly knocked her approval ratings down from an all-time high of just three months ago, according to a new poll.

While her favorability rating in February was 61 percent, a new Quinnipiac University poll out Friday had it cobbled down to 52 percent and her once double-digit lead over potential GOP presidential challengers Jeb Bush and Sen. Rand Paul has been cut to less than 10 percent.

"Her score is down substantially from her all-time high score in February. The drop in her favorability is substantial among men, Republicans and independent voters. One reason for her drop may be that 48 percent of voters blame her either a little or a lot for the death of the American ambassador in Benghazi," said Peter A. Brown, assistant director of the Quinnipiac University polling Institute.

The drop in her favorability rating follows a series of GOP-led congressional hearings into the State Department's mishandling of the Benghazi affair. More are planned and lawmakers have demanded that Clinton's top political aides at State appear to testify.

Still, she is the Democrat's best chance to succeed President Obama in the Oval Office. In matchups with the leading Republican hopefuls, Clinton beats Paul 49 percent to 41 percent and Bush 48 percent to 40 percent.

Vice President Joe Biden is her chief rival for the job. But in the new poll he loses to Bush by six points and Paul by four points.

"If Ms. Clinton chooses not to run in 2016, the potential Democratic field could include a somewhat unpopular vice president and a number of new faces who are unknown to the vast majority of Americans," said Brown. "The potential Republican candidates include many unknowns also. Some of them, however, lead the incumbent vice president and outscore him when it comes to overall voter favorability."