To my knowledge the last time this happened was in 1824 when the Democratic-Republican Party failed to unite behind a single candidate for President.
Jeff Greenfield, in a forward-looking article this past week-end, reported Republican Party leaders are aghast at the prospect of Donald Trump as their candidate. In order to protect some semblance of a viable party for the future there is talk of forming a third party. At least one expert believes such a party's candidate could beat Trump in several states.
That prospect leads to speculation no candidate would command a majority of Electoral Votes, throwing the decision to the House of Representatives. Whether that would be the current House or the House elected in the fall of 2016, I am not sure.* I will research this and report back later.
For now, things are getting interesting behind the Christmas lights and beneath the tinsel.
*Up-date: See comment below