“First gentleman” is pretty well established. That seems to be what most (all?) governors’ husbands have been called.
Yes. Etiquette did dictate the office prior to becoming president when addressing him. However, when was the last time you heard Gov. Reagan or Gov. Carter? So like all the others over the last 40+ years It will be President Clinton or President Bill Clinton to distinguish which.
We’ve recently had the problem of distinguishing which of The Bushs was being referred to. Too me it was simple. I always referred to the old one as… The Elected Bush.
Bush the Elder and Bush the Usurper.
First Mate…? 
In honor of Prince, he should be called TAFKAP. The Adulterer Formerly Known As President.
Regards,
Shodan
There is a scene in the film “Amistad” in which John Quincy Adams, who during the events of the movie sits in Congress some years after being President, is referred to as “Mr. President.”
I was surprised at this and thought it an error - I thought it a modern convention - but when I looked into it, found it was probably historically correct. The convention of referring to former Presidents as “Mr. President” predates Lincoln.
Despite this, every self-proclaimed reference on etiquette says it’s wrong. That said, I’m not sure where they get this from, and I wonder if maybe one source said this and all the references date back to that one. There’s no formal rule in a U.S. code on how Presidents, sitting or former, are supposed to be addressed; it’s custom, no more or less legal than how former boxing champions are often addressed as “Champ.”
The Former HMFIC
The Protocol School Of Washington.
Miss Manners. Google Books link. Can’t copy and paste.
Definitely not if your name is Mr.Trump 
This is what The Washington Post appears to have settled upon. So WJC would be the First Gentleman of the United States but generally referred to as Mr. Clinton.
Big Pimpin’ Bubba
First Stud
President’s Husband Of The United States. PHOTUS.
The Best Friend a Comedy Writer Ever Had?
Anyone else note the irony in this serial liar, cheater, likely rapist of at least one woman and committer of sexual assault against others being called “Gentleman”?
Anyone else note the irony in this serial liar, cheater, likely rapist of at least one woman and committer of sexual assault against others being referred to as “Gentleman”?
Most likely, the news media will call Hillary “President Clinton” and Bill “Former President Clinton”. I’m betting “First Gentleman” will be limited to tabloid and morning shows, stand up comedians, and other very informal discussions.
But if we ever have a woman president whose husband isn’t a former president himself, we’ll probably hear “First Gentleman” quite often.
That’d be my guess. There is something of a precedent, with George H.W. and George W. Bush, and John and John Quincy Adams. However, neither John Adams nor George H.W. Bush were part of their sons’ households, like Bill would be. So I suspect copy editors wouldl avoid calling Bill “President Clinton” unless it’s completely unambiguous which President Clinton they mean.
Apologies for the double post. The second was intended to be an edit of the first.
The content needs apologizing for more than the double posting.