I don't think it was the Us Against Them people who gave Trump the win, though. There were the moderate Rockefeller Republicans who didn't want their taxes to go up and who figured that even though Trump himself was a piece of shit, a Trump Presidency "really couldn't be that bad." Plus folks on the left side who didn't really want a Hillary Presidency and who also figured Trump couldn't be that bad, and folks on the moderate left who figured there was no way Trump was going to win anyway. And even with all that, it took Comey blatantly violating FBI protocol twice, including a week before the election, and even with all *that*, it was basically a tie in the three states that gave Trump his electoral college win.
Now, everyone (except the Us vs Them folks) knows that a Trump Presidency *really is that bad*. So the moderate Republicans are either for Biden or at least won't vote for Trump. The people on the left are also strongly willing to hold their noses and vote for Biden to get Trump out. And because Barr has no credibility, any kind of October Surprise from DOJ or the FBI will not really have much persuasive value.