It looks like the Mattis bubble is bursting. That was probably inevitable, but it is still a bad sign.
As discontent has mounted among Republicans, some have been suggesting that the party could draft an outsider as its nominee at the convention in Cleveland this summer. Some have been calling for famed (retired) Marine General James Mattis to run. Unhappiness with the idea of a Donald Trump nomination has even, according to Tim Mak in the Daily Beast, led a group of wealthy Republican donors to consider drafting Mattis to run as a third-party candidate if Trump gets the nomination.
The idea isn’t that Mattis could win the nomination, but that he might win enough states to throw the election into the House of Representatives, which is what happens if no candidate gets an outright majority of the Electoral College. At that point, under the Constitution, the House gets to pick from the top three candidates. (But it’s not a straight-up House vote — each state gets a single vote in the proceeding.)