Sen. Marco Rubio’s support among Republican voters has dropped 15 points since February, shortly after he took a high-profile role in advocating comprehensive immigration reform, according to a new Rasmussen poll.

The survey, of 1,000 likely voters conducted June 20-21, found that 58 percent of Republicans nationwide view Rubio favorably. That is down from Rubio’s 73 percent favorable rating among Republicans in mid-February. Rubio introduced the Gang of Eight immigration initiative in the last days of January.

The intensity of GOP support for Rubio has also waned. In February, 44 percent of Republicans said they had a very favorable opinion of him. In the new poll, that number is 21 percent.

The decline in Rubio’s favorable rating appears related to his decision to lead an effort — reforming the immigration system — that few believe the government will actually achieve. “Most voters favor the concept of comprehensive immigration reform but do not believe that the government is likely to try and enforce the border security provisions of any new law,” Rasmussen writes. “Many have viewed Rubio’s role in selling the reform plan as convincing conservative voters that the border security provisions are acceptable.”

As for other voters, Rubio’s favorable rating among Democrats has also gone down, but it has gone up among independents. In February, 20 percent of Democrats and 37 percent of independents had a favorable impression of Rubio. In the new poll, 16 percent of Democrats view Rubio favorably, while his rating among independents has climbed to 41 percent.