'It's over for me': Rick Santorum pulls out of Republican race to give Romney clear run

Daughter's health cited as decisive factor as party focuses on battle to oust Obama from White House

Rick Santorum, standard bearer of the social conservatives, yesterday effectively pulled out of the Republican presidential race, making certain what has long been obvious: that Mitt Romney will be the party's nominee to face Barack Obama in November.

At a hastily convened press conference in Gettysburg, the former Pennsylvania senator who has emerged as Mr Romney's last serioius rival, announced that he was suspending his campaign. "It's over for me," Mr Santorum declared, but he vowed to keep up his fight for conservative principles.

Though the timing of the announcement came as a surprise, its thrust was not. A string of primary victories by the better organised, better financed Mr Romney, and the prospect of several more in a fortnight's time – including what could be an embarrassing defeat inflicted on Mr Santorum in his home state – has banished all doubt about the outcome of the battle.

But the immediate reason may well have been a family one, the condition of the Santorums' three-year old daughter Bella, who suffers from the rare genetic disorder Trisomy 18 and was back in hospital at the weekend. "It caused us to think, about the role we have as parents," Mr Santorum said, referring to his wife Karen who stood beside him yesterday. Significantly however he did not mention Mr Romney by name in his 12-minute speech, let alone endorse him – a sign of the long-visible tensions between the two men.

The news nonetheless was a huge relief for the Romney campaign and for the Republican establishment that has rallied behind him. The former Massachusetts governor will now be free to focus exclusively on what will be an uphill struggle to unseat Mr Obama.

Last night Mr Romney heaped praise in on his vanquished opponent. Mr Santorum had been an "able and worthy competitor," and "an important voice in our party", he said.

For Mr Santorum too the decision makes eminent sense. Athough he won 11 primaries and caucuses, he had no realistic chance of amassing the 1,144 delegates needed to secure the nomination at August's Republican convention in Tampa, Florida. By contrast, Mr Romney already has more than 650, more than all his opponents combined.

In recent days even Mr Santorum's Christian conservative base had shown signs of swinging behind Mr Romney, in the interests of the greater goal of recapturing the White House. For months, polls have shown that despite (or perhaps because of) his suspect conservative credentials, Mr Romney has the best chance of defeating Mr Obama in the general election, when independents and moderates will have a crucial say.

By quitting now moreover, Mr Santorum comes across as a good party man, thus preserving his longer term ambitions. Still only 53, he is young in political terms, and in his speech yesterday he left no doubt he will not be retiring into private life anytime soon.

Coming from nowhere a year ago, he achieved startling success. From a meagre financial base, he staged a late surge to win January's caucuses in Iowa that kicked off the nominating season. He followed up with wins in the mid-west and several southern states. Had Newt Gingrich not remained in the race, thus splitting the conservative vote, Mr Santorum might well have won key primaries in Michigan and Ohio. Had he done so, Mr Romney himself might have been knocked out of contention.

As it is Mr Santorum could be well positioned for a presidential run in 2016 (if Mr Romney loses this November) or in 2020, given the Republicans' habit of awarding their nomination to the second-placed finisher the last time around. If the two can overcome their personal animosity, he could be a tempting 2012 vice-presidential nominee, who would shore up Mr Romney among social conservatives.

Pressure now will be intense on Mr Gingrich – whose support has dipped into single digits in the most recent primaries – to follow Mr Santorum's example and pull out. If he does, the last contender standing would be the quirky libertarian Ron Paul, who by his own admission has not the remotest chance of actually winning the nomination.

Instead yesterday marked the effective end of an extraordinary primary season, in which Mr Romney was the favourite throughout, but who never convinced. One rival after another – Michele Bachmann, then Rick Perry, then Herman Cain, then Newt Gingrich, and finally Mr Santorum – briefly overtook him, only to either self-destruct or be overwhelmed by Mr Romney's superior organisation and resources.