Donald Trump is favored to win the Iowa Republican caucuses Monday night; he’s not a heavy favorite, but our polls-plus and polls-only forecasts give him a small advantage. Trump is also the candidate unacceptable to the most Iowa Republicans, according to the latest poll from the Des Moines Register: 37 percent said they would be “not OK” with Trump winning the Republican nomination.

How does that make any sense? Trump isn’t liked by many Republicans, but he’s loved by a few, and in a 12-candidate field, that may be enough.

Trump is a divisive figure among likely Republican caucus-goers. His favorable rating, 50 percent, is nearly matched by his unfavorable rating, 47 percent. He is far more unpopular than Ben Carson, Ted Cruz and Marco Rubio.

Favorable ratings vs. support in Des Moines Register poll CANDIDATE FAVORABLE UNFAVORABLE SUPPORT Ben Carson 72% 22% 10% Marco Rubio 70 21 15 Ted Cruz 65 28 23 Donald Trump 50 47 28 Jeb Bush 41 53 2 Chris Christie 40 44 3 Rand Paul 40 41 5 John Kasich 28 27 2 The DMR poll did not include favorable/unfavorable ratings for the other four Republican candidates. Source: Des Moines Register

More than that, he has become more unpopular since August. Trump’s favorable rating has dropped by 11 percentage points, and his unfavorable rating has risen by 12 points.

Normally, this type of trend line would suggest that Trump’s support on the ballot test would be falling too. Instead, Trump’s 28 percent in the latest Des Moines Register survey was the highest he’s ever earned in that poll. Running a regression on the favorable ratings and ballot test results in the DMR poll reveals a weak relationship — only 21 percent of the variation in a candidate’s polling percentage is explained by his or her favorable rating.

But you can see what’s going on if you break down the favorable ratings by “very favorable,” “mostly favorable,” “mostly unfavorable” and “very unfavorable.” Trump scores a 27 percent “very favorable” rating — just behind Cruz’s 29 percent and Carson’s 28 percent and ahead of Rubio’s 25 percent. The relationship between candidates’ “very favorable” ratings and the ballot test is far stronger than when you combine the “very favorable” and “mostly favorable” ratings — the “very favorable” ratings explain 68 percent of the variation in the ballot test numbers.

Trump himself has seen little change in his “very favorable” rating. Since August, it’s consistently been between 25 percent and 27 percent. The two candidates who have overtaken Trump in Iowa polls since August, Carson and Cruz, have seen much more volatility in their “very favorable” ratings: Carson’s has ranged from 28 percent to 53 percent, and Cruz’s from 28 percent to 43 percent. Both are near their low points for the period in the latest Des Moines Register survey.

The “very favorable” ratings in this race seem more meaningful than each candidate’s overall favorability, which maybe shouldn’t be surprising in such a crowded field. Carson and Rubio, in particular, have broad appeal but a much smaller group of core supporters.

Trump would almost certainly lose the Iowa caucuses if the field of candidates were smaller. Just 7 percent of Iowa Republicans list Trump as their second choice, while 17 percent list Cruz and 20 percent list Rubio. The Des Moines Register poll found that likely Republican caucus-goers preferred Cruz over Trump in a one-on-one matchup 53 percent to 35 percent.

The problem for this majority is they’ll never get to vote in a two-man race. In a field of 12 candidates, it’s all about core support. You don’t get to cast a negative vote.

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