The second trend disfavors Trump. Since modern public-opinion polling began in the 1940s, every American president has enjoyed the support of a majority of Americans for at least a moderate stretch of time — except Trump. When he was inaugurated in January 2017, his initial job-approval rating was split at 44 percent approve, 44 percent disapprove, according to the RealClearPolitics average of the major polls. It quickly fell into net negative territory, where it has remained ever since.

This is probably due in part to the political polarization of the 21st century. Strong Democrats were never going to approve of Trump, at least not for long. However, strong Democrats alone do not make up half the electorate. The critical groups for either side are unaffiliated independents and soft partisans. Trump has consistently struggled to win these people over.

This is unprecedented. Even presidents who end up being enormously unpopular — Harry Truman, Jimmy Carter, George H. W. Bush, and George W. Bush —enjoyed lengthy periods of popularity. Their tenures fell into disrepute because events got the better of them. Trump, on the other hand, has received low marks from the start, suggesting that Americans were wary of him at first and have never reconciled themselves to his administration.