Republicans don't like Trump as much as they used to

A low net favorability rating lowers the ceiling on Trump’s support. Indeed, in three of the four live-interview polls that asked voters about their second choice since the debate (CNN, Fox News, NBC/Wall Street Journal and Suffolk University), Trump trails Ben Carson when you combine Republican voters’ first and second choices.

Of course, Trump’s popularity could improve. It has, after all, gone up before. And campaigns are long; before Newt Gingrich faded for good from the 2012 campaign, for example, he experienced multiple surges.

At this point in the campaign, however, Trump’s popularity is far lower than you’d expect from a future nominee. Most nominees (not including incumbent presidents) have either been very popular or not well-known at this stage.1 Trump’s well-known and not very popular.