Bush is not a clown.
Cruz is not a clown.
Rubio is not a clown.
All three have solid credentials.
Santorum and most of the others should not be classified as clowns, but rather as lightweights and under qualified.
All three are unabashed climate change deniers. All three publicly supported Indiana's Religious Freedom Restoration Act. Bush likes to talk about how much he likes "scientific racist" Charle Murray, and he's tripped all over his clown shoes on the Iraq War. Ted Cruz's public advocacy for theocracy put him in the clown car even before he pulled a Strom Thurmond on Obamacare while reading Green Eggs and Ham. Rubio dog-whistles creationists about how old the Earth is, when he's not busy telling everyone how he thinks ISIS and Iran are on the same team.
They're all evil idiot clowns, and they will all willingly keep doing whatever slapstick they think will get them votes from the right wingnuts, no matter how stupid it is.
Regardless of your personal vehemence towards and your virulent contempt for these public servants, all three are very intelligent, competent, and well educated, and would be capable Chief Executives.