On Thursday, Public Policy Polling released its latest 2016 tracking poll of Iowa Republican voters. The results show a dramatic shift in Republican voter sentiment. Sen. Marco Rubio, who had led in previous surveys, has dropped to 5th place. Sen. Rand Paul now leads the pack in the critical first-caucus state.

Sen. Rand Paul leads with support from 18% of Republican voters. Following him are Gov. Chris Christie (16%), Rep. Paul Ryan (15%), former Gov. Jeb Bush (14%), Sen. Marco Rubio (11%), Sen. Ted Cruz (10%), former Sen. Rick Santorum (6%), Gov. Bobby Jindal (2%) and Gov. Susan Martinez (1%).

PPP’s last 2016 survey in Iowa was conducted in February. Sen. Rubio’s support has dropped 5 points since then. Since the February poll, Rubio has been the most public supporter of the Senate amnesty bill, legislation that is increasingly unpopular with the Republican base.

Among the more vocal opponents of the Schumer/Rubio bill are IA Sen. Chuck Grassley and IA Rep. Steve King. Getting on the opposite side of these two popular lawmakers doesn’t seem to be a winning strategy in the Hawkeye State.