After 19 debates, eight caucuses and primaries, and tens of millions of dollars in – mostly negative – advertising, it’s half-time in the Republican nomination battle. By this point, it was meant to be all over, with apparent frontrunner Mitt Romney predicted to have it wrapped by the end of January.

But his rivals – and the party’s conservative base – have displayed a stubborn determination to force the contest all the way to the final play, the convention in August in Tampa, Florida.

Rick Santorum was the first to upset the script when he came from nowhere to narrowly beat Romney – eventually – in Iowa. And he was back in spectacular fashion this week, with a clean sweep of Colorado, Minnesota and Missouri. Newt Gingrich, meanwhile, enjoyed a huge victory in South Carolina that also underlined serious doubts among conservatives about Romney.