Early on Biden characterized himself as a transition candidate, meaning that he will serve a single term at most. There is widespread speculation that due to his age and health, he may not complete his first term.

I think in the eyes of many Republicans the conservative media successfully portrayed Biden as being a pawn.  That may be too strong of a word, but there was definitely a sense among Republicans that he is not the one calling the shots.  

So who is?  If you listen to the conservative media (I believe Fox news is still the #1 network) its the far left.

Kamala Harris (his hand picked successor) has been portrayed as having the most liberal voting record in the senate.  Bernie Sanders has publicly stated that Biden's campaign pledged to adopt large portions of Bernie's platform, and that Biden would be the most progressive president in history.  And there is a huge narrative surrounding the AOC wing of the Democratic Party rising to prominence as more moderate establishment Democrats are voted out.

Both sides characterized this as a crossroads election.  So to answer your question, I think many Republicans held their noses and voted for Trump again not because they were enthusiastic about him, but rather, because they were voting against the far left.  

Sure, Trump has had a dependable base on the far right that would support him no matter what, but in the aftermath of the riots, many of them feel betrayed because he invited them to the capitol and then condemned them after the violence.  That may or may not hurt him with respect to his base.

More importantly, I think Trump's conduct post election has caused most moderate Republicans to reach their breaking point regarding their ability to support him.

If the election were held again today, I think he would get far fewer votes, even with the far left as his perceived opponent.  

In a Republican primary where he is running against legit conservative candidates, I don't think he could win again.

Trump has shown that he intends to remain active in politics, but I think he is done as a candidate for office.

This is all about power and political games.  I suspect that defending Greene had more to do with protecting her committee seats and creating a narrative that Dems are hypocrites (for kicking Greene out over controversial views and remarks, but not removing Omar for the same thing) than it did with anyone actually agreeing with her viewpoints.

Their support also feeds the narrative that Republicans support free speech (even controversial, unpopular opinions), whereas Democrats are out to destroy our civil liberties and censor everyone who disagrees with them.

So my point is that what these guys are doing in Washington is not indicative of how the average Republican thinks or would vote.  I myself am a conservative, and I find Greene's comments deplorable.  I think her removal was appropriate, and I would not support her if she were running for office in my state.