Hillary Clinton was on the ballot in 2016. She was a below par candidate. Her net favorability (favorable – unfavorable) rating of -12 points in the exit polls was not only vastly below then-President Barack Obama’s net approval rating (+8 points), but her net favorability rating was below that of the Democratic Party as a whole (-2 points). Trump won on the backs of voters who disliked Clinton more than they liked Trump.
In 2018, Trump wasn’t running against any single candidate. He was, if anything, running against the Democratic Party as a whole. The Democratic Party as a whole wasn’t all that more popular than they were in 2016. They were more popular than Clinton in 2016, though.
This year, Biden, the standard bearer for the party, is about as popular as the Democratic Party as a whole was in 2018. His net favorability in live interview polls since the convention stands at +2 points, which is nearly identical to the +1 points the Democratic Party had in the 2018 exit polls as well as the -2 net favorability rating it had in 2016. Biden’s ratings are far better than Clinton’s in 2016.
The only thing that seemed to have mattered to the Republican Party’s election hopes in the last four years has been Clinton’s unpopularity.