Last week we wrote about Democratic ambitions to pack the U.S. Supreme Court. This week the Electoral College is on the chopping block as Sen. Elizabeth Warren comes out in favor of its abolition, Beto O’Rourke makes sympathetic noises and Colorado’s Democratic governor signs a bill adding his state to the “National Popular Vote Interstate Compact.” Scrapping the system the U.S. has used to select presidents since its founding will likely soon be the Democrats’ default position.

Like the Supreme Court, the Electoral College sometimes frustrates the will of political majorities. But while “majority rules” has always been an appealing slogan, it’s an insufficient principle for structuring an electoral system in the U.S.

Presidential elections often do not produce popular majorities. In 2016, neither Hillary Clinton nor Donald Trump won 50 percent. “Plurality rules” doesn’t have the same ring to it. In the absence of the Electoral College, the winner’s vote share would likely be significantly smaller than is common today. Third-party candidates who can’t realistically win a majority in any state would have a greater incentive to enter the race.

Democrats are upset that Trump is president with 46 percent of the vote to Clinton’s 48 percent. What if a Republican was elected with a third of the vote in an election featuring five formidable third-party candidates? A free-for-all plebiscite would hurt the system’s legitimacy. The Electoral College helps narrow the field to two serious contenders, as voters decide not to waste their vote on candidates who have no chance to win.

The founders designed the Electoral College to help ensure that states with diverse preferences could cohere under a single federal government. Anyone who thinks this concern is irrelevant today hasn’t been paying attention to the current polarization in American politics. The Electoral College helps check polarization by forcing presidential candidates to campaign in competitive states across the country, instead of spending all their time trying to motivate turnout in populous partisan strongholds.

In a popular-vote contest in 2020, for example, the Democratic candidate might ignore the economically dislocated areas that Trump won and focus on urban centers along the coasts. Trump might campaign more in upstate New York or Texas but ignore urban voters.

FROM AN EDITORIAL IN THE WALL STREET JOURNAL