Joe Biden and Donald Trump are both aiming only at a narrow win

The presidential campaign is at knife’s edge. Both parties assume patterns of support will closely resemble those in 2016. And both are making surprisingly little effort, considering how close that contest turned out to be, to increase their levels of support.

The past three years and 10 months have seen little outreach by President Trump to most of those who didn’t vote for him in 2016, particularly to the college-graduate suburbanites who tipped the House to Democrats in 2018.

He seems unwilling or unable to squelch the undisciplined tweets and...