In the event Hilary Clinton is elected president of the USA, it is correct to address him as Mr. Clinton.
As Miss Manners points out:
The president's spouse is a private citizen with no official rank, and thus is properly addressed, in writing and in person, as Mrs. Washington (with neither her nor her husband's given name; she would be the Mrs. Washington, with no danger of being mistaken for Mrs. Chuck Washington).
And now to the husband. If anything is sillier than "first lady," it is "first husband" (unless this is necessary to distinguish him from a marital successor also on the scene). He would be the host, and addressed simply by his name and "Mr." or another honorific he held, such as general or governor.
Perhaps this is the place to say once again that American protocol dictates that only one person at a time can hold the title of president of the United States. Former presidents should never be so addressed, although they have even taken to calling one another that. Miss Manners would have thought that having reached that position would surely have cured anyone of status anxiety.