"In reality, how credible is Trump? Is all this bluster and American exceptionalism what voters are actually looking for?"
Yes, for some he is a laughing stock. But for the fox news watching, everything is someone else's fault, Obama is a Muslim traitor to the USA crowd this is exactly what they want to hear.
And remember he isn't playing to the population as a whole, he's only got to convince republican supporters right now.
If he gets the republican nomination a lot of republicans will vote for him even if they think he's crazy because the alternative is a democrat winning.
US politics: where they put the stories that are too absurd for reality TV.