With 75 percent of Republicans not voting for Trump, a candidate can still hold the plurality so long as the "no" vote is divided among a sufficient number of alternatives.

This is a logical point about plurality voting: a candidate with about 25% support can win a plurality if the remaining 75% is split among enough rivals that none of them exceeds 25%. True: the arithmetic holds (it does whenever no single alternative exceeds the leader's share), and Trump's Republican primary support in 2015 polling was roughly 25%, meaning about 75% were not backing him (allowing roughly 20–33%). Mostly true: the logic holds, but Trump's polling share at the time differed somewhat from 25% (for example 30–35% or 15–20%). Mixed: the logic holds, but the 75% figure was badly off for the time. Mostly false: the reasoning is misapplied, for example because the rules in question are not plurality-based in a way that matters. False: the logic is shown to be invalid.

Set before the research began.

1. E1 GOP presidential primary: why wild swings persist The Christian Science Monitor · 3 November 2015

   “October 10: Trump 22.9, Carson 17.7, and Rubio 9.9”

2. E2 GOP presidential primary: why wild swings persist The Christian Science Monitor · 3 November 2015

   “Sept. 22: Trump 28.0, Carson 19.0, and Rubio 8.0.”

3. E3 Poll: Donald Trump back on top, with Ted Cruz climbing into second CBS News · 10 December 2015

   “Thirty-five percent of Republican primary voters support Trump, up 13 points since October, and his highest level of support in CBS News polling.”

The plurality arithmetic holds: a candidate near 25% leads as long as no single rival tops that share. In the evidence, 2015 GOP primary polling had Trump at 22.9 on October 10 and 28.0 on September 22, with the nearest rival (Carson) at 17.7–19.0 (E1, E2). Both figures fall within the roughly 20–33% band the criteria allow. One CBS poll in December had him at 35% (E3), but most of the evidence fits the claim that about 75% of Republicans were not backing him.