Romney prepares for the vital primary he can't afford to lose

After a round of fundraising in New York, Mitt Romney was yesterday pouring money into television advertising in Illinois, whose primary on Tuesday he cannot afford to lose as he struggles to fend off Rick Santorum, his main conservative rival for the Republican presidential nomination.

A Chicago Tribune poll last week showed Mr Romney with a narrow lead in Illinois – but that was before Mr Santorum's triumph in Alabama and Mississippi. They may not have tipped the race decisively in his favour. But they ensure that a contest that Republican strategists had hoped would by now be over will now drag on, perhaps all the way to the convention in Tampa in late August.

"Look at the maths," is the mantra of Romney aides, who point to their man steadily gathering delegates even in states he does not win, thanks to the proportional system used in most primaries thus far. Indeed, despite his third place finishes in both Mississippi and Alabama, Mr Romney netted more delegates on Tuesday than Mr Santorum, thanks to his victories in Hawaii and American Samoa which held caucuses the same night. Right now, Mr Romney has roughly 500 delegates, double his closest rival and well ahead of Newt Gingrich.

Even so, delegate maths does not guarantee a Romney win. It may be impossible for either of his rivals to secure the absolute majority of 1,144 needed in Tampa – but it is possible Mr Romney may not do so either. If so, Republicans would be facing their first open convention since 1976, when Gerald Ford held off Ronald Reagan.

And even if he does win, Mr Romney will have done so in unappealing and bloody fashion: not by generating grassroots enthusiasm, but by crushing his opponents with his financial and organisational muscle.