He’s polling at about 45% (plus or minus about six points), but that 45% only counts the ~66% of people who actually vote. So it’s only 28-33% of the population that actively supports him enough to vote for him.

It can still be close but that is close between the people that vote. More than half of all Americans do not vote consistently. We don't have mandatory elections, so if half the country doesn't vote and its close between the two candidates, then its close between two quarters of the population, not half. And it seems maybe a little pedantic, but those half of people who don't vote are either disenfranchised or implicitly choosing neither candidate. Half the voting population is not half the population; those non voters are actual people. Maybe if they were treated as an important part of the electorate, they would vote. Maybe they wouldn't vote for a republican or a democrat, in which case it is also in the dems best interest to disenfranchise voters, although that certainly isn't the conventional wisdom, nor is it the mission of the millions of volunteers who work to sign people up to vote on important issues.

He was technically less popular at this same point in the 2016 election. He can absolutely still win if things go the same way that 2016 did. Liberals didn’t fucking vote in 2016, (for a variety of reasons), which handed the win to Trump.