What does Romney have to do to stay alive? Candor compels me to say that I don't really know but am about to offer my opinion anyway.
1081 delegates are at stake. It looks to me that, if Romney and Huckabee can keep McCain from getting over half of them, it counts as a win - maybe even a big one. McCain will still have a sizeable delegate lead but he won't be close to over the top. Because the expectation is that he emerges as unstoppable tonight, he loses if he doesn't win big. (But spin control is going to be crucial.) If it is played right, McCain's money and support as "inevitable" falters and Romney lives to hope for an anti-McCain backlash. It will be, incidentally, a huge test of whether the MSM loves McCain or a horse race more.
In addition, Romney has to get a very solid majority of what McCain does not get. This is necessary both for his own nomination scenario and to put pressure on Huckabee to quit. His continued presence in the race and capture of delegates hurts Mitt.
Finally, he can't just do this by running strong seconds. He needs some wins. It seems to me, though, given the number of GOP delegates awarded to state winners, that he is highly unlikely to accomplish the first two without achieving this as well.
How can he do this? He is going to get dusted in some big winner take all (or mostly all)states like New York and New Jersey. It seems clear that he needs a big win in California where he is going to have to take the lion's share of the congressional districts. He needs to win big, as he is expected to, in Utah and Massachusetts, but he also has to pick off a few other states. Georgia would be huge. He needs to take the Colorado and West Virginia caucuses. At least one more win would be nice, but I am hard pressed to see where it will be.
But, if he does this much, and can get some delegates from more proportionally allocating states like Illinois and Tennessee and have Huckabee clean up in Arkansas, maybe steal "winner take all" Missouri from McCain and score delegates in places like Oklahoma and Alabama, Romney could get close to a best case scenario.
But the math is tough. There will, of course, be some unpledged delegates, but it's for hard for me, right now, to see Romney with more than 300 and Huckabee with more than 120.
I think that keeps Romney alive but may also make Wisconsin his last stand.
An update tonight.