Check the TL in my sig...
While I'll admit that we're not at the convention yet in Gone The New Hope, John Anderson is indeed the stop-Reagan candidate in that TL.
In GTNH an utterly bungled Bush race early in the year gives Reagan the "Big Mo" and Anderson receives a lot more press. He might turn off conservative Republicans and confuse open minded Democrats, but he's intriguing enough to be the second place candidate for the entire primary season. You should also know that in GTNH Carter has failed miserably by 1980 and Kennedy (following a car accident that necessitates him stopping his campaign) endorses Gov. Jerry Brown.
Jerry Brown becomes the Democratic nominee and Reagan leads in the Rep. primaries, while Anderson is second. Bush and Kennedy are out.
I can't spoil too much because we're not there yet, but I can say that if Anderson is treated as he was in my TL and if Bush endorses him to stop Reagan, and then Reagan suddenly gets out for some reason (for this challenge, let's say he has an accident and doesn't think he'll recover in time to go to the convention), Anderson would default win at the convention - provided he acts more conservative than he actually is, picks a popular and very conservative VP... and no one can agree on a dark horse.
After that, Anderson will be going head to head against Carter (Brown in my TL, but in yours, I'll assume Carter), but pretty soon the Republicans would get wise to some of Anderson's more liberal beliefs and start shittin' kittens. (This will inevitably happen, Anderson at some point during this time came out with confessions of an awful lot of social and foreign policy progressivism. He'll scare the shit out of the base right after they nominate him.)
What happens next is anyone's guess. Does the base launch a third party campaign with a true conservative?
Doesn't matter.
Anderson may lose a lot of Republican support, but he'll probably also attract a lot of Democrats and Independents.
In a two way race against a very unpopular Carter, Anderson will probably win by a narrow margin. (I predict voter turnout will be lower than OTL.)
In a three way race where the conservative base pulls out of Republican support it's harder as it will likely confuse and split Republicans.
However, if Anderson plays his cards just right and paints Carter as a good man but a failed president, and the third party IndieCon as a sore loser, while also managing to attract support from independents (whose votes actually win elections), Democrats, and of course party-loyal Republicans, I could see the election being a nail biter with a possible Anderson win. Whoever wins will win by a pubic hair out of a three way split electorate, however.
It's not really a good start to a presidency, being just barely the nation's choice out of THREE tickets, but it sets up some really interesting political WIs to follow, particularly as the IndieCons who jumped ship have now successfully launched the most successful third party attempt maybe ever, and also have federal matching funds and an eye on 1984. Exciting shit, man. I love it.
I rambled, I apologize, but I hope the first part helped a little, at least.