Let’s assume the Democrats’ basic premise is true, i.e. that Trump lost fair and square. Trump’s loss wasn’t terrible - a couple of hundred thousand votes short in the swing states that decide the White House race. This is in the face of two outlier events - a mass casualty pandemic and the resultant economic depression representing the worst downturn since the Great Depression.
The Democrats expected a complete sweep of the states, both at the White House and Congressional levels. FDR got a 413 electoral vote victory margin. Biden’s was 74. The 1932 House elections gave the Democrats got a 196-seat margin, vs the ~12-seat margin they got in 2020. The 1932 Senate elections moved the Democrats to a 22-seat margin, vs the 1-seat margin (thanks to the VP tie breaker vote) they just got after the 2021 GA runoffs. This was a blue wave a toddler could safely paddle in, not a tsunami.
That’s why they’re trying to prevent Trump from running again. He’s no Herbert Hoover, whose political career was over the day the results came in. The Dems aren’t afraid Trump will get the 2024 GOP nomination and lose in the general. They’re worried that one hiccup or other before 2024 will send Trump back to the White House with commanding GOP majorities, but this time cleansed of the never-Trumpers who gave him so much trouble in his first term.
If Trump intends to run again, the interval from now until presidential season should involve the installation of Republicans who support the Trump agenda in the midterms, and the removal of those who don’t. Bannon’s quest to populate elected offices with Trump supporters needs to resume, so that when Trump re-enters the White House, his agenda is ready to go from Day 1.
Recent behavior (massive election fraud, more recent cancel culture, etc.) suggests they will.