Two polls released last week showed Mr. Rubio leading the governor by 18 percentage points in the August primary, a reversal from last summer, when the former Florida House speaker trailed Mr. Crist by 30 points.
The shifting fortunes underscore how profoundly President Barack Obama’s slumping popularity is convulsing both parties. The rise of hard-line conservatives and Tea Party activists are eroding support for Democrats and moderate Republicans.
“The conservative movement is the one seemingly with all the energy right now,” said Matthew Corrigan, a political scientist at the University of North Florida. “That really puts moderate Republicans with targets on their back.”