It's all over for the Republican hopeful Rick Santorum - who has announced the end of his campaign, after phoning the front runner Mitt Romney to admit defeat.

Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.

It was astonishing that he lasted this long in the race: outspent, out-organised and eventually outclassed, the former Pennsylvania senator Rick Santorum chose his home state to announce he was suspending his presidential campaign.

Speculation had been rife all day about his future in the Republican race for the White House: the precious momentum that had propelled him this far was rapidly dwindling. In almost every key primary contest, the clear front runner, Mitt Romney, had been steaming ahead in the race to amass enough delegates to win the nomination outright. Even Santorum's staff began admitting openly they didn't know whether he'd be carrying on or not.

Santorum was pinning his final hopes on Pennsylvania, which holds its primary later this month, but although he began with a double-digit lead, the polls soon began turning against him. Then came a more personal conflict: his three-year old daughter Bella was rushed to hospital over the weekend, forcing him to suspend his campaign events. The child suffers from a rare chromosomal condition that interferes with her development.

His campaign announced earlier today that the candidate would go back on the trail, but with his chances of becoming the eventual nominee virtually zero, on top of his family worries, his decision suddenly changed. Tonight he emerged in front of reporters in Gettysburg, flanked by his family, to make his announcement.

It had been a difficult weekend, he said, after days at his daughter's hospital bedside, and said it had given the family cause to think. He spoke of his fear that the American dream was slipping away, and said that as a good parent, he'd wanted to take on the responsibility for changing that, on behalf of children across the country.

He spoke of the stories he'd heard on the campaign trail, from people who'd inspired him to carry on his campaign. "Not my story, but their stories, were what fuelled our campaign and raised our energy", he said. "We were winning, in a different way". He insisted there could be no strong economy without strong families and "moral fibre."

Santorum even managed to joke about his trademark sweater vest - a tanktop to British readers - which, he said "became the official wardrobe of the Santorum campaign", after the Twittersphere turned him into an unlikely fashion icon.

On a more serious note, he claimed that speaking up for the voices of ordinary people meant he had been able to come from nowhere: "Miracle after miracle, this race was as improbable as any presidential race, and I thank God for that", he said, and insisted he'd been right to focus on social conservative issues which often got him into trouble during the campaign.

For weeks the Republican hierarchy has been urging the party to unite around Mitt Romney and call off the deeply divisive and expensive primary campaign. Another conservative, Newt Gingrich, is now technically in second place, but even he admitted at the weekend that Romney was pretty much certain of winning the nomination.

As for Barack Obama, he has already begun focusing his political fire against Romney: fighting November's presidential election in all but name. Now, with Santorum gone from the race, the phoney war is over. All the Republicans have to do, is find some enthusiasm at last, for their man.

Felicity Spector writes about US politics for Channel 4 News