I've been saying for a while that Trump the President is not a good fit for Montana like Trump the candidate was.
Montana has a Libertarian bent so Authoritarianism doesn't fly here. Bullock barely outrunning Biden is not that surprising since Polarization is off the charts here this year. Moderate Repubs that used to cross over for Bullock and Tester are basically closet Dems now (see former Gov Racicot and Former SOS Bob Brown). Split ticket voting will be less this year but turnout will be massive.
If you look at the cross tabs the people in this poll were 52% Trump and 36% Hillary and 13% didn't vote in the last election. That jibes with the internal Dem numbers I've seen. The head of the MDP told me once that MT is 52% Repub and 36% strong Dem so you have to run the table with independents and peel off a few moderate pubs to win statewide.
Montana also has a fairly strong anti-incumbent bent, regardless of candidate or party. Nixon ‘72 was the last time it gave an incumbent a larger margin in his re-election bid than the first time he ran.