Does President Donald Trump believe in God?

Yeah, he believes he is.

LMFAO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

he's too rich for that ****

His behavior suggests that he does not.

The fact of the matter: Yes: That is why he backs Israel and is a true believer of God The Lord Jesus Christ our Lord and Savior holy word the bible.

Not sure, he might. As far as I know, it is not an absolute requirement to be a believer in God for a person to be president of the USA.

How many past presidents ever claimed to be believers in God?

Presidents  Obama, Clinton, Carter, Ford, Nixon for example never claimed to be believers/christians even though they like all other presidents would frequently use the phrase "God bless America" 

Donald Trump was elected by christian and non-christian citizens to be president of the USA.

Trump is certainly no Christian. To be Christian one must seek forgiveness, and Trump said he has NOTHING to seek forgiveness for.

Probably not. He's always been either an atheist or agnostic or certainly someone completely unconcerned with religion. Now he claims a fake Christianity just for votes. After all, those Evangelical votes put him in the White House. 

it is not whether people believe in God that is important but whether God believes in them

He probably believes that God has a sense of humor for bestowing COVID-19 on him.

He's 70 so probably. It was just the done thing back then. But then again he's a new yorker so maybe he's just full blown atheist and hiding it from the evangelicals.