The known (and unknown) unknowns in the GOP race ahead

Under traditional rules of thumb, one would expect that many Trump fans won’t actually vote, and that his percentages will be well under the 33 percent he’s getting in national polls and the 25 percent and 29 percent he’s polling in Iowa and New Hampshire.

That in turn suggests he’ll have a low ceiling of support in later contests, since many, perhaps most, of non-Trump respondents have unfavorable feelings about him. In which case a candidate who emerges as Trump’s chief rival, or one of two candidates who rise to the top, will be nominated, much as candidates have been in the past.

But maybe Trump supporters will actually turn out in large numbers, even those who haven’t been engaged in the past. Evidence for that includes the large crowds he’s been attracting and the huge viewership numbers for the Republican debates: 13 million to 24 million, far above the previous record of 8 million.