Former Florida Gov. Jeb Bush comes in second place at 16 percent.
Rubio's support has jumped 7 points, putting him behind only Trump.
Sanders leads by huge margins with independents and young voters.
Support for both senators has risen in a new national poll.
Trump has 41 percent support with Cruz at 11.
The poll showed Clinton leading by 18 points last month.
Trump has support from nearly half of GOP voters at 48 percent, while Cruz has 16.
Only 23 percent said that when the question was asked in March.
Trump has 29 percent support in the state, and Rubio has 15 percent.
A third of white evangelicals surveyed support Trump.