And the first country thinking of going to war with the U.S. because of Trump is: Iran?

Maybe

That has to be the operative word here.

Why?

Because of Trump's statements about Muslims.

So, threatening U.S. ships and causing them to fire warning shots likely is a warning to the American People:

"Don't elect Trump or we will shoot up your ships!"

However, Iran is not the only Muslim Country that hates Trump.

All Muslim countries do.

IN fact, I sort of expect one or all Muslim countries (if Trump gets elected) likely will try to do away with Trump. Will they succeed? LIkely not in a country like the U.S.

However, it might be important to understand the full blatant hatred toward some of the things Trump has said to 1.5 billion Muslims of all sects at this point.

So, will Iran, Saudi Arabia and other Muslim countries actually fight the U.S.?

That's hard to say in the end.

However, it is likely they all would cost the U.S. a whole lot of money (billions and possibly trillions) in lost business for American Businesses if Trump was elected.

Why?

Because Middle Eastern People take insults very seriously and they always hold a grudge against all who slander them.