Yeah there are multiple reasons this breaks down but fundamentally it is the responsibility of leaders to convince voters to vote for them. If they fail to do so that’s on them, not the voters.

Also, in tight elections there are always a large number of possible constituencies that could swing the election. It does not follow that they’re individually responsible for the outcome.

Especially, since, y’know, as a leftist who typically does vote for democrats it’s not as if I personally control what other leftists do.