I know I always say that polls are less useful than the media makes them out to be. And I know I also say that it's way too early to think about the next presidential race. But this Public Policy Poll of Iowa strikes me as very interesting:

PPP's newest look at the Republican race for 2016 in Iowa finds a new leader. Rand Paul is at 18% to 16% for Chris Christie, 15% for Paul Ryan, 14% for Jeb Bush, 11% for Marco Rubio, 10% for Ted Cruz, 6% for Rick Santorum, 2% for Bobby Jindal, and 1% for Susana Martinez. Paul also led the last time we polled New Hampshire with 28% to 25% for Rubio and 14% for Christie.

Marco Rubio had led the way when PPP polled Iowa in February, but has dropped 5 points since then even though his favorability rating is basically unchanged (54/13 then, 54/14 now). Candidates rising since then are Christie (up 4 points and also from 36/33 to 45/27 on his favorability), Paul (up 3 points and from 55/19 favorability to 60/15), and Ryan (up 5 points and from 63/16 favorability to 68/12).

The only reason that Rubio's polling could have dropped so much over the last four months is immigration. The only noteworthy thing he's been promoting is his immigration reform bill. And if support of immigration causes at least a five-point drop in poll numbers among Republicans, we could be looking at the ugliest, most racist Republican primary in recent memory next time around. All the usual caveats apply—it's three years out, we've got a midterm election between now and then, the whole electoral landscape will likely look different, etc.—but I wonder what Republicans are going to do if their internal polling shows dismal numbers like this for any candidate who dares to reach out to someone who's not white, Christian, and straight.