Cambridge, Mass. — DONALD TRUMP has won Republican primaries in 23 states to date — far more than any of his opponents. Yet in the first 17 states he won, several of the other major candidates might well have beaten him in a one-on-one contest.

There is no contradiction here. In the early contests, Mr. Trump attracted less than 50 percent of the vote (in Arkansas he got only 33 percent); a majority of voters rejected him. But he faced more than one opponent every time, so that the non-Trump vote was split. That implies he could well have been defeated in most (given his extreme views on many subjects) had the opposition coalesced around one of his leading rivals. In such a scenario, he might have been out of contention long before he could ride his plurality victories toward his first outright majority win — in New York, last month.

American primaries are not the only recent elections to produce winners lacking the support of a majority of voters. In India, the Bharatiya Janata Party received only 31 percent of the vote in the last general election, but got a majority of parliamentary seats. (Even including political allies, their vote share was no more than 39 percent.) The B.J.P., a right-wing party with a Hindu ideology for which only a minority of Hindus voted, has been running the government since, which is fair enough, given the electoral system. But it has also been persecuting political dissent as “anti-national.” Even majority support doesn’t give leaders in a democracy a right to stifle dissent. Invoking the battle cry “anti-national” in the name of the entire nation seems especially pernicious from a government without majority support.

As with the Republicans and Mr. Trump’s flirtations with fear and violence, India now suffers the ill effects of a serious confusion when a plurality win is marketed as a majority victory. The Muslim Brotherhood government of 2012 to 2013 in Egypt provides another, and similarly disturbing, example; it helped to undermine democracy in Egypt altogether.