NBC and the Journal didn't poll Tea Party voters in April, but in February, the group's approval of Rubio split 52 percent to 8 percent. This month, it's at 47percent to 15 percent.

Following the immigration battle in the Senate, Rubio has championed both a new abortion bill and a threat to shutdown the government if the president's signature health care plan isn't defunded. Both measures are seen as an attempt to regain support with the conservative base, which has largely opposed the immigration push.