The clever thing about the Mitt Romney campaign's
claim that it would take "an act of God" for Newt Gingrich or Rick Santorum to win a delegate majority is that they directed attention away from the question of what it would take Romney to achieve a delegate majority—at least a majority through primaries alone.
It's obvious just by looking at the primary calendar and the delegate allocation rules (which are mostly proportional) that as long as either or both Newt Gingrich and Rick Santorum are candidates, the delegate battle will continue for at least two more months, and more likely will continue at least until June.
But short of both Santorum and Gingrich dropping out and conceding to Romney, what would it take for Mitt Romney to secure a delegate majority and therefore win the nomination? Nate Silver took a rigorous look at the same question as applied to Rick Santorum, but his analysis actually can be used to answer the question about Romney.
According to Nate's projections, the most likely scenario at this point is that Mitt Romney will win about 45% of the remaining vote, putting him in position to hit the magic number of 1,144 on June 5, assuming super delegates are prepared to put him over the top at that point. Even if the super delegates stayed on the sidelines, he'd secure enough delegates from electoral success by June 26.
So if the question is whether it would take an act of God for Mitt Romney to secure a delegate majority, the answer is no. If things continue pretty much as they have been, Romney will be able to secure the delegate majority without super delegate help.
At the same time, however, it wouldn't take an act of God to deny Romney a delegate majority.
If he does better than expected, Romney could potentially secure the majority at some point in May, but if he does even 5 percent worse than Nate's baseline scenario, he wouldn't be able to secure the delegate majority without help from super delegates. That's a very plausible scenario, but it starts moving Romney into danger territory because it would mean Romney had effectively lost the second half of the primary season to Rick Santorum.
The scariest scenario for Romney is the one in which he does even worse than that. Neither he nor Santorum would end up with enough delegates to win the nomination, even with the help of super delegates. Fortunately for Romney, that's the least likely scenario, but it's not so out of the realm of possible that you'd say it required an act of God.
In all likelihood, Romney will grind out a win, securing the delegates he needs without needing to cut a deal. But there are plausible, if unlikely, scenarios under which Rick Santorum could deny Mitt Romney a delegate majority. Those scenarios would give Santorum huge influence over Romney, and might even give Santorum a shot at securing the nomination himself (though it would probably take something close to an act of God for that to happen). And as long as those scenarios remain plausible, it would take an act of God to get Rick Santorum to quit the race.