Mr. Rell has evidently decided to not be a public figure here in CT. As such, he is rarely mentioned in any media. If any clarification is needed, it is usually only some formation such as “…the governor’s husband…”
He’ll be known as the neutered ex president if Hillary catches him fooling around again. 
I think the White House would have taken pains to avoid that. They would not have wanted to leave the impression someone else was in charge. “President Bill Clinton,” maybe- but I suspect a different compromise would have been reached.
Bear in mind that, contrary to popular belief, “First Lady” is not the title of the President’s wife. Rather, it is the title of the hostess of the White House. If Hillary had been elected President, most likely the function would have been filled by Chelsea. I feel sure that it would not have been Bill.
While there probably would have been some jocular references to Bill as the First Gentleman, in general he likely would have continued with his actual title of Former President, upgraded to the courtesy title of Mr. President when that would not cause confusion or be barred by protocol.
Ireland has had two women presidents - one still in office. Their husbands have no standing in the eyes of the state or of the people. There is no provision in the constitution for such a thing. The idea of the wife or husband of the president having any official, or even semi-official role, would be quite bizarre. They remain private citizens.
The president, however, when in office is formally addressed as (in Irish) A Shoillse or (in English) Your Excellency. The spouse is simply Mister or Mrs. X
Miss Manners is using the same logic that George Washington had : “There is only one President, but there are many Generals”
Hence upon leaving office,
President Washington becomes General Washington
President Bush becomes Governor Bush
Governor xyz stays Governor xyz
Judge xyz stays Judge xyz