Rick Santorum joins crowded Republican field for president
Rick Santorum, a Christian conservative who came second in the 2012 Republican primaries, has launched a second campaign for the US presidency.
Mr Santorum launched his campaign on Wednesday at an event in his home state, Pennsylvania.
The former senator won several key races in 2012, emphasising social issues like abortion and gay marriage.
But he may have trouble standing out in the crowded the field of 2016 Republican candidates.
Santorum stuck to his key themes of traditional family structure, increased support for middle-class working families and lower taxes in his speech.
"As middle America is hollowing out, we can't sit idly by," Santorum said. "We don't need another president who is tied to big government or big money. Today is the day we begin to fight back."
He also talked about supporting US war veterans and getting them access to healthcare quicker.
Santorum said if he is elected president, the US "will defeat ISIS".
Analysis: Anthony Zurcher, BBC Washington
If history were a good judge, Rick Santorum's 2012 second-place campaign performance should have left him well positioned for a 2016 bid to capture the party's top prize.
Mitt Romney went from runner-up in 2008 to nominee in 2012. John McCain took silver in 2000 and gold in 2008. George HW Bush, Bob Dole, even Ronald Reagan - all turned earlier losing efforts into eventual Republican nominations.
And yet Mr Santorum is already being treated by much of the media as a 2016 also-ran, and he registers toward the bottom of the pack in polls and money raised.
In early appearances he's tried to blend his trademark evangelical conservatism with foreign policy experience gained during his tenure in the Senate and a blue-collar pitch to working Americans. It's a combination that could distinguish him in this crowded field - but he's up against a formidable assortment of well-funded fresh faces and established names this time around.
Mr Santorum will compete against candidates like former Arkansas Governor Mike Huckabee, Texas Senator Ted Cruz and retired neurosurgeon Ben Carson, who have all been actively courting Mr Santorum's base of socially conservative and religious voters.
The sheer number of candidates for the White House has created logistical issues for debate moderators.
Fox News, which will host the first Republican debate, has decided to the limit the field to 10, based the candidates' standings in recent national polls.
Mr Santorum, who would just qualify for the debate based on recent polling, took issue with the Fox News decision, calling it arbitrary.