It’s not official until he’s formally nominated at the convention in late August, but for all practical purposes the Republican presidential contest is now over and Mitt Romney is the nominee. Rick Santorum, the fundamentalist ex-senator from Pennsylvania who was his last serious rival, conceded defeat overnight and suspended his campaign, although he has not officially endorsed Romney.

The next big contest was in Pennsylvania on April 24. Santorum was running neck and neck with Romney in polls there, and evidently decided that, given that he no longer had a chance at the nomination, withdrawal now was a better look than risking defeat in his home state.

Romney, who was joint runner-up (with Mike Huckabee) for the nomination in 2008, has been the favourite since about this time last year and never really looked likely to lose. Nonetheless, Santorum did remarkably well overall, carrying 11 states and giving Romney some moments of serious anxiety.

While that’s a sad commentary on the state of the Republican Party, I don’t think it had anything much to do with Santorum’s own qualifications, which were and always remained pretty thin. As Jon Chait puts it, his “success was entirely the function of his being a Republican not named Romney who happened to be there when every other alternative had either been destroyed by Romney’s money or collapsed on its own”.

But while it was largely a matter of luck that this particular extremist got within striking distance of Romney, it was always likely that some extremist would. Even well into the campaign Romney had very low approval ratings for a front-runner; the party’s base remained suspicious of him as a moderate at heart who was counterfeiting a conservative image.

It’s another question as to how much this will hurt him against Barack Obama in the general election. The direct effect is likely to be small; they might not like Romney, but with rare exceptions the Republicans will obediently turn out to vote for him, given that the alternative, as they see it, is another term of Kenyan Muslim socialism.

The real problem for Romney is that by having to run hard to the right so late into the year in order to sew up the nomination, he has given the Democrats plenty of ammunition. There are now endless video clips of Romney desperately trying to prove his far-right credentials that probably won’t play so well with swinging voters: expect them to feature prominently in Obama’s advertising over the next seven months.

That’s especially serious for Romney because he has a reputation for fairly abrupt changes of front. The makers of Etch-a-Sketch are already reaping a windfall after his spokesman used their product as a simile for how positions could be re-oriented for the general election campaign; any further tweaking of Romney’s views will need to be handled with extreme care.

The long primary campaign has also exposed non-ideological weaknesses in Romney. He never came across as a very likeable candidate, often appearing strained or wooden, and he seemed to have a particular sort of tone deafness on issues of wealth. In a campaign where economic issues are going to be uppermost that could prove a serious handicap.

And what of Santorum now? Several times, particularly in the early primaries, he seemed to be pitching for a vice-presidential slot, but it’s hard to imagine Romney taking such a risk. Another run in 2016, however, is quite likely, and runners-up have a good record at their next attempt (including John McCain and Bob Dole, as well as Romney himself); given that he did so well this time with such meagre resources, Santorum could well fancy himself next time, in what might be an easier election without Obama to worry about (assuming, of course, that Romney falls short in November).

But before getting carried away with that scary thought, it’s worth remembering the list of qualified Republicans who chose not to enter the field this time: Huckabee, Mitch Daniels, Chris Christie, Paul Ryan and more. Santorum was lucky to get the gig as the “anti-Romney” this time, but lightning rarely strikes twice in the same place.