If Clinton was elected President in 2016...

[President Johnson]

Doubtful. Not sure whether Trump could have sustained his cult of personality. Of course the Republican Party would not have gotten any less insane after a 2016 defeat.

Obviously the answer also depends on how close 2016 was.

[President Johnson]

The Republican establishment likely would've ensured that Trump didn't receive the nomination again. Trump would've had a harder time keeping his base enthusiasm alive for four years if he wasn't actually president.

How would they do that? The Republican establishment has lost control over its base a long time ago. It's the base that selects the candidate for president. Trump might not have been the nominee in 2020 after a defeat in 2016, but it would have been some other guy on the staunch right.

[President Johnson]

I voted for Clinton in 2016. If she had won in 2016 I don't think she would have run in 2020. I think she had plans to make a one term pledge had she won. Of course we will never know now.

Nobody is voluntarily just serving a single term. Especially no one that wanted to be president for decades.