Coming 2nd or better in the primaries. The idea that he needs to become President to avoid embarrassment is nonsense. It's really, really hard to become President, and getting a major party nomination is far better than what the vast majority of politicians achieve.
You act as if the guy has never run before. The calculus is entirely different for someone who has already failed twice.
Hence "2nd or better", rather than say, "4th or better". Like I wouldn't say that someone like Gingrich had an "embarrassment" of a campaign, although I probably would if he'd been the Republican nominee before. If I'm Romney and I really want to be President, even if I think the chances of me eventually winning are less than 10%... that's not bad. It's much better odds than what many other hopefuls have every cycle. It's not an embarrassment to take those odds but fall a little short.