That depends on what his goal is. If he wants to actually win the Presidency, then it’s already too late: There are enough key states whose deadlines have already passed that there’s no realistic way to win without them. On the other hand, if his goal is just to punish the Republicans for not choosing him, then he can do that regardless of sore loser laws, since there are enough key states without those laws to leave the Republicans with no realistic chance.
No, there aren’t. I believe you are confusing primary filing deadlines (the one in Illinois just passed) with general election filing deadlines. John Anderson withdrew from the Republican primaries and announced an independent candidacy on April 24, 1980, and still succeeded in getting on the ballot in all 50 states.
He had to sue a handful of states which attempted to enforce an earlier general election filing deadline, and he won in every case; see Anderson v. Celebrezze.
I’m not expert on the laws of all 50 states, but I don’t believe “sore loser” laws apply to the presidency in any of them. John Anderson, again, was on the ballot in just about every state that had a Republican primary in 1980, and managed to get on the general election ballot in all of them.
After further research . . . it appears that “sore loser” laws DO apply to presidential candidates in at least some states. Michigan applied a sore loser law to keep Libertarian candidate Gary Johnson, a Republican convert, off of the ballot in 2012. Johnson had announced as a Libertarian in December 2011, but failed (apparently because of carelessness) to withdraw from the Michigan Republican primary until after the deadline in February 2012. The denial of access was upheld by a federal circuit court and apparently not appealed to the Supreme Court.
Sources disagree on the number of states with presidential “sore loser” laws, probably because the law in all states isn’t entirely clear.
I honestly don’t think it matters. Even if he doesn’t get the nomination and he doesn’t get on the ballot, I think he could be a significant write-in candidate. Hell, many of his supporters seem to love him so much that even if he announces he’s dropping out completely, I would not be surprised if he still got significant votes as a write-in. Now, in either case, when I say “significant” I don’t mean that he has a chance at winning; I simply mean he may very well have the potential to affect the outcome.
Even there, he’s still got some hoops to jump through. In Colorado, for instance, in order for write-in votes to be counted, the candidate has to file an Affidavit of Intent with the Secretary of State. Otherwise, all write-ins are just lumped together.
In many states, you have only a very short time to withdraw from the election, once you file for it. Like 7-10 days from the closing of filing, even though the vote can be months away.