Would the following people have won re-election if they could?

[Stranger in a strange land]

The first three would have won if they ran, but Reagan would not have run and Ike most likely would not have.

Everyone except Bush.  If Kennedy hadn't been assassinated, then he would have, too.

That's hard to say, because there's no way of knowing what a 2nd JFK term would have looked like.

Bush

ROFLMAO

The question with Dubya is how badly he would have lost.