Thompson isn't leading man material, never has been. He's a character actor. He plays the avuncular southern lawyer or the ... avuncular southern politician. He has played the president or head of the CIA or whatnot from time to time, but they were all small featured parts. There's a reason for this --- he's not believable in the lead. He has the charisma of a number 2 pencil.
They should have consulted some of their successful show business friends about this before putting so much hope into their Ronald Reagan sequel. (I'm sure their A-list --- Shannon Doherty, Bo Derek and Patricia Heaton --- would have been happy to consult.) Note to GOP: if you are going to keep "casting" your presidents, hire a casting director.