Then retire home for a mint julep and a good cry.

The real question, if not Trump or Clinton, who then?

Any RW vote lost to Trump is a gain for Dems. Only two people have a chance to be POTUS and a non-red vote is a de facto blue vote, because it reduces the number of votes needed by one. Obviously twice as good is any RW vote that votes blue in protest, as that reduces the number of votes needed by two compared to a baseline race.

Unless a credible intraparty spoiler emerges (which is possible in both D and R races this year, but only a hypothetical right now) neither Trump nor, most likely, Clinton could give a rat's ass about Green or Constitution or Libertarian etc candidates. They know that it's incredibly unlikely they will matter. Only Nader has ever managed to make a (terrible) difference in generations playing spoiler from the current fringe parties and that was only by a rare confluence of election fraud, terrible Dem campaign choices, ballot confusion and media venality.

So Graham votes for the Libertarian or writes in McCain? Not going to shift a single EV.

Could this change? Sure. The Reps could draft an establishment candidate spoiler like Romney, knowing that it will guarantee a Dem White House win but would prevent both 2016 downticket and future Rep candidates with being tarred by Trump's foul association. Sanders could (v. v. unlikely) scorn his reputation for honest integrity and do the same on the blue side after promising not to. He'd guarantee a Trump WH but without the concomitant brand saving aspect for Dems. Since he's already raised his profile and influence enormously there is nothing positive he could hope to achieve. And sure to really go to the extreme in unlikeliness, Clinton could lose the nomination but choose to run anyway against Sanders and Trump. Again, bugger all in it for her as it too would guarantee a Trump win. Only the first option is even worth considering frankly, and that would be just peachy for Dems.

Barring those three options, Trump knows any non-Clinton (probably) vote is a win for him, and vice versa. Whose name is on it really doesn't matter much at all.

If your the Dem and a third party Dem runs, like Sanders, Clinton would definitely care. Likewise, if your Trump and a Romney or other GOP establishment member runs on a third party platform, Trump would care.

What part of "If your on of the two major party nominees, you would." is incorrect?

Do you suppose Graham realizes that?