Analysis: delegate numbers adding up against Mitt Romney's rivals

With victory in Illinois Mitt Romney draws ever closer to the Republican nomination. Here we examine the numbers he needs to seal the deal.

How close is Mitt Romney to winning?

In terms of delegates he's about half-way there, having so far racked up 522 of the 1,144 needed to take the Republican nomination. Of the 1,324 delegates still up for grabs the former Massachusetts governor needs to win around 47 per cent to guarantee his place on the ballot in November. Mathematically, that should be well within his grasp.

But harder to measure are the intangibles of momentum and inevitability. A quicker and sexier route to the nomination would be to finally deliver out knock-out blows that force his rivals to drop out altogether and concede defeat. As yet, there's no sign of that. He won big in Illinois but both Newt Gingrich and Rick Santorum are vowing to keep fighting on. Right it looks like Romney is going to have make the long and slow climb delegate by delegate.

Could Rick Santorum or Newt Gingrich still clinch the nomination?

Yes, but the climb is so steep as to be all but impossible. To win the nomination outright Santorum needs another 891 delegates. That means he has to win 67 per cent of all the 1,324 delegates still up for grabs.

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.