Our tracker of voters’ intentions shows the contest behind Trump

To see how extraordinarily tight Donald Trump’s grip on his party is, look back . Then Mr Trump was the unexpected front-runner in the Republican presidential primaries, polling at around 30%. That was still uncertain enough for to call his candidacy a “long shot” in . Today, according to of Republicans’ voting intentions, he has double the support he did then. His closest rival, , the governor of Florida, is on a lowly 12% (see top chart). Of all the things that could stop Mr Trump from contesting next year’s election, the most probable obstacle is himself.