WASHINGTON (AP) - Rick Santorum has never been shy about picking fights - even with fellow Republicans.

Just two months after arriving in the Senate in 1995 as Pennsylvania's junior senator, an upstart Santorum and some other conservative senators tried to strip Oregon Republican Sen. Mark Hatfield of his powerful Appropriations Committee chairmanship because of his deciding vote to oppose a balanced-budget amendment to the Constitution.

Santorum made no apologies. It was a matter of sticking to his conservative principles, he said.

"I try to stand up for what I believe in and I always will. I don't run around looking for a fight. I just stand up for what I'm elected to do," the brazen Santorum said then, elected to the Senate at age 36. He would rise to the No. 3 position in Senate leadership before a crushing 18-point defeat in 2006.

With the Iowa presidential caucuses on Tuesday, Santorum is hoping to spring a surprise showing by casting himself as the only "consistent conservative" among his GOP rivals. He's been stuck at the back of the pack for months, but he's steadily visited every Iowa county and pressed for support from Republicans with doubts about the conservative credentials of other candidates, especially Mitt Romney and Newt Gingrich.

Polls show Iowans warming up to him, albeit late in the contest, and he's in third place in some surveys.

"I think I have a shot and I'm feeling better about that shot every day, the top three," Santorum, 53, said at a diner in Independence, Iowa. "This could be a late-breaking race. Now we just have to get over the hurdle of convincing people we can win."

A devout Catholic and father of seven, Santorum is driven by his belief that religion deserves a stronger role in public life. Raised in blue-collar Butler, Pa., he is the son of an Italian immigrant father.

A lawyer, he won a House seat in 1990 against a seven-term incumbent using political skills he'd first sharpened as an undergrad at Penn State University. He soon shot to prominence as a member of the so-called Gang of Seven - freshman Republicans who bucked the House leadership to expose fellow lawmakers who abused checking privileges at the now-defunct House bank.

The scandal helped the GOP capture the House in 1994, the same year Santorum beat Democratic Sen. Harris Wofford and emerged as a rising GOP star.

In his congressional career, Santorum championed fiscally conservative measures, including a balanced budget amendment. He railed against big government and was the author of a sweeping welfare reform bill in 1996. He also earned a reputation as a hardliner on social issues by successfully pushing a bill that banned late-term abortions and saying in 2003 that he believed states had the right to ban gay sex or other private behaviors "antithetical to a healthy, stable, traditional family."

His confident style wasn't always appreciated by Pennsylvanians, some of whom didn't like comments he'd made on social issues, including comments in a book criticizing some working parents. His 2006 Democratic opponent, Bob Casey Jr., successfully accused him of pursuing a rigid ideology that put him out of step with voters.

By the time of his defeat as part of an anti-war, anti-incumbent tide, even some conservatives were frustrated with Santorum. Some saw him as too much a part of the big-spending establishment and others didn't like that he chose to endorse Arlen Specter, then a moderate Republican senator who years later would switch to the Democratic Party, over conservative Pat Toomey in the state's close 2004 Republican primary. Specter barely won.

After he left office, Santorum and his wife of more than two decades, Karen, had their youngest child, Isabella, who was born in 2008 with trisomy 18. Fewer than 10 percent of those diagnosed with the genetic disorder live past their first birthday, and Santorum laments frequently on the campaign trail that he wishes he was home with her. Another child born to the couple, Gabriel Michael, died in 1996, two hours after an emergency delivery.

In Iowa, the scrutiny on Santorum will likely grow if his campaign continues to gain momentum. On Thursday, Texas Gov. Rick Perry at a coffee shop in Washington, Iowa, questioned Santorum's conservative credentials. Perry said Santorum in the Senate loaded up federal legislation with so-called pork-barrel spending for his home state and called him a "prolific earmarker."

Santorum defended the practice in an interview with CNBC, saying it was allowed under the Constitution and that he owed it to Pennsylvanians to appropriate money for their state. He said it later became abused and that he'd support a ban on earmarks if president.

Taking - and dishing - political zingers is nothing new to Santorum, who acknowledged on the Senate floor before he left office in 2006 that sometimes his style had hurt him.

"Maybe I spoke up too often, too loudly, too boldly on some of the things my employer didn't agree with me on," Santorum said. "I hope they respect the fact I felt ... it was a heartfelt disagreement, and I did what I did and I said what I said because I believed it was in their best interest, even though they may not have thought so."

_____

Associated Press writer Mike Glover in Independence, Iowa, contributed to this report.