Clinton holds a narrow lead over Bush, 47 percent to 45 percent, and leads Rubio 50 percent to 43 percent, according to a Quinnipiac poll released Friday.

The former first lady also tops the other possible Republican candidates in the poll. She leads New Jersey Gov. Chris Christie by 4 points, Wisconsin Rep. Paul Ryan by 8 points, Kentucky Sen. Rand Paul by 10 points and Texas Sen. Ted Cruz by 16 points.