For Gingrich the task is even more daunting. He's currently on 135, just over 10 per cent of the total he needs for the "magic number" of 1,144. That means of the remaining 1,324 he needs to win 1,009. It would take a miracle and the window is closing rapidly.
What happens if no one reaches 1,144?
This is certainly a possibility. Gingrich and Santorum have almost no hope of winning outright but they could do enough to keep Romney from reaching the finishing line. If that happens we head to a "brokered convention" in Tampa in August, where the wise old men of the Republican party will try to cut deals to make deals to pick a nominee and avoid a civil war.
Who would win at a brokered convention?
Given his strong lead in delegates and his backing from the Republican establishment, it's hard to see how Romney could be denied the nomination at a brokered convention. The question is what deals would he have to make in order to get his rivals to fall in line? One distinct possibility is that he could be forced to accept Santorum as a running mate.