Trump primary challenge odds

[Mr. Morden]

What is the relative probability of these six scenarios?:

1) Trump is no longer president by the time of the 2020 Iowa caucuses
2) Trump is still president in 2020, but is not running for reelection, at least by the time the primaries start
3) Trump runs for a second term in 2020, but fails to win the Republican nomination
4) Trump runs and is re-nominated, but with less than 65% of the nationwide Republican primary vote
5) Trump runs and is re-nominated, with 65-85% of the nationwide Republican primary vote
6) Trump runs and is re-nominated, with more than 85% of the nationwide Republican primary vote

For context, keep in mind that Obama got 89% of the 2012 Democratic primary vote, while running against complete nobodies.  So one would think that for any primary challenger of any real consequence whatsoever, holding Trump to under 85% shouldn’t be *that* difficult.

Also for context, the last “major” primary challenger to a sitting president was Buchanan in 1992, and that one was:

Bush 73%
Buchanan 23%
everyone else 4%

[The Other Castro]

1. 10%
2. 7%
3. 3%
4. 20%
5. 40%
6. 20%

[Dr. MB]

1) Trump is no longer president by the time of the 2020 Iowa caucuses – 15%
2) Trump is still president in 2020, but is not running for reelection, at least by the time the primaries start – 1%
3) Trump runs for a second term in 2020, but fails to win the Republican nomination – 5%
4) Trump runs and is re-nominated, but with less than 65% of the nationwide Republican primary vote – 30%
5) Trump runs and is re-nominated, with 65-85% of the nationwide Republican primary vote – 40%
6) Trump runs and is re-nominated, with more than 85% of the nationwide Republican primary vote – 30%

4, 5, and 6 would depend on who's running. If Ted Cruz, John Kasich, or any other major figure decides to challenge Trump in 2020, it would improve the odds. If nobody does but Jack Fellure, the odds for 4 and 5 are about 0%.