If, for example, Hilary Clinton becomes President, will Bill re-enter the White House as 'the First Gentleman of America'?
There's no official title of First Lady, and hence there can be no official equivalent.
The White House may favour a particular term—and quite likely opposition pundits will favour another—, but whether "First Gentleman", "First Spouse", "First Consort", "First Husband", or "First Man" wins out, will be a matter of competing terms in a language rather than anything we can confidently predict now.
The possibility of a former First Lady becoming president colours things, because the US has the unusual practice of using the title President for former presidents. Hence while "First Lady" is used as both a description of the rôle and as an (unofficial) title, it is likely that in this particular case the title President would mostly be used as an (honorary) title, as it is now.
Personal opinion here, and I'm not an American but then neither are Barrie England or Jon Hanna.
My instincts tell me that if Hilary Clinton were to be President of the USA, her husband Bill Clinton would still be referred to as "former President of the USA". I checked and sources seem to confirm this.
Is a Former President Addressed as President (name)?
I have been directing people to refer to former presidents as President (last name).
Is that correct?
--- Anna McD
Dear Ms. McDonald:
This issue is complicated since we hear former Presidents referred to as President Clinton and President Bush on the media all the time; Here's what is the correct formula as it appears in my book
Former President of the United States [...]
This is the traditional approach for any office of which there is only one office-holder at a time. So, with officials such as mayors, governors or presidents ... only the current office holder is addressed as Mr. Mayor, Governor, or Mr. President ... formers are not addressed that way. That's not to say some reporter might not call a former mayor Mayor Smith or a former president President (Surname). But doing so is incorrect and confusing to the public. The former office holder is no longer due the precedence and courtesies we extend to the current office holder. He or she speaks with the authority of a private citizen. We honor former office holder's service, but the 'form of address' -- which acknowledges the responsibilities and duties of office -- belongs only to current office holder. With offices of which are many office-holders at a time ... senators, admirals, judges, etc. addressing 'formers' with their former honorific not disrespectful to a singular current office holder.
To explain the correct form I would say "using the title of a former position is flattering to the former official and he or she may not correct you, but is not respectful to the current office holder. There's only one "(name of the office)" at a time." Source
The following piece of advice actually claims it is acceptable and correct to refer to an ex-President as simply as Mr (Surname/Lastname) This could well be the case if Hilary Clinton should ever win the election to be the first woman president of the US. Her husband would then be referred to as Mr Bill Clinton.
When addressing a former President of the United States in a formal setting, the correct form is “Mr. LastName.” (“President LastName” or “Mr. President” are terms reserved for the current head of state.) This is true for other ex-officials, as well.
When talking about the person to a third party, on the other hand, it’s appropriate to say, “former President LastName.” This holds for introductions, as well: A current state governor is introduced as “Governor Tom Smith,” while you’d introduce an ex-governor as “former Governor Jim Bell.” Source
Wikipedia informs us: "As of February 2014, there are four living former presidents" and it also tells us: The youngest living former president is Bill Clinton, born August 19, 1946
My belief is that Bill Clinton would be referred to as the "former President of the USA". As an honorific it is more dignified and respectful than First gentleman (which I find facetious); "Mr Bill Clinton" (he's not a nobody) or worse, The President's husband.
From a 2007 Washington Post blog entry by Peter Hauck:
In an appearance at the Aspen Institute's Ideas Festival on July 7, Bill Clinton is asked what he would like to be called if Hillary is elected. His response: "First Laddie." It appeared that he was kidding.
Sorry, couldn't resist.
I guess that would depend on which reporter/news flunky is the first to blab about the thing on television, rather than anything else.
The situation has never come up before, so I seriously doubt there's an official document describing it (I'm not sure if there's anything that makes the title of "first lady" official, and how that one came about, research into that could lead to an answer for the reverse case).
Of course in the future if there's ever a homosexual couple in the white house, that would also need to be covered.