Sen. Rick Santorum (search) is a rising Republican star Democrats desperately want to take down in 2006.

State treasurer Robert Casey Jr., (search) his likely Democratic opponent, is ahead in state polls. He's quietly raising millions for what is expected to be the closest Senate race in 2006.

Casey, like Santorum, opposes abortion, and he has name recognition from his late father, Gov. Robert P. Casey. He was recruited to run by national party leaders seeking to take out a Republican Party leader.

"This is going to be a race that's going to be viewed as a national referendum. This is a nationalized Senate race," said David Thornburgh, executive director of the Pennsylvania Economy League, Southeastern Pennsylvania.

Santorum, a conservative from Pennsylvania who is chairman of the Senate Republican Conference, is promoting his new book, "It Takes a Family." An energetic and tenacious politician, in recent weeks he has earned the ire of liberals for comments in his book, which criticizes feminism for instilling in women that it is more gratifying to work outside the home than stay home with children. It also compares abortion (search) to slavery.

The book is ranked 13th on the New York Times bestseller list, and has sold more than 40,000 copies, according to the publisher, ISI Books.

Democrats accused him of flip-flopping recently when he said he had no intention of running for president in 2008; then, two days later, he said he was going to leave open the possibility.

Earlier this summer, he was criticized for meeting with Terri Schiavo's parents in Florida before her death. And, in a rare attack on the Senate floor, Massachusetts Sen. Ted Kennedy lashed out on Santorum for a column he wrote three years ago linking Boston's liberalism to the sex abuse scandal in its Catholic diocese.

Santorum's rhetoric has alienated some voters like Neil Cohen, 62, of Pittsburgh, a conservative who worked on Santorum's last campaign, who says he'll vote against him next year.

"This nation was founded on religion, but it's not run on religion and I believe he's attempting to now and he will attempt to run this nation on a religious basis," said Cohen, who works at a law firm.

Santorum said people might not support him on every issue, but he's a known quantity who delivers for Pennsylvania.

"People know what I stand for and why I stand for it," Santorum told The Associated Press recently in an interview at the Aspinwall Bookstore outside Pittsburgh where he was promoting his book. "I don't think that's the case with my opponent."

Casey, who served two four-year terms as state auditor general, said he offers a different approach for Pennsylvania.

"I'm going to be focused on Pennsylvania's priorities, not Washington politics and the scorched earth partisanship and the intolerant ideology that you see too much of in Washington," Casey told the AP in a phone interview from his car. "Frankly, Sen. Santorum's been a big part of that, and it's all about divide and conquer and pulling people apart instead of bringing them together."

Santorum has said he expects to raise $25 million for the campaign. Between April and June, he raised $3.6 million and reported $5.7 million cash on hand. Casey reported raising $1.9 million in the period, and had $1.6 million cash on hand.

People who have written Santorum off underestimate what a tough campaigner he is, said Robert Maranto, a political science professor at Villanova University

"It's funny how many people have told me the race is over. It's a year out. It's way out," Maranto said. "Santorum is one of those guys like Bill Clinton, like Richard Nixon, who will do anything to win."

Santorum's style appeals to some voters who like that he's a straight shooter. Ken Heiss, 64, of Mount Washington, said Santorum is misunderstood.

"I know what he prefers for himself, but he doesn't go around telling other people they have to be that way," said Heiss, president of Spectrum Computer Inc., who stood in line to have Santorum sign his book.

Casey received the most votes of any candidate in state history in the treasurer's race in November. But he's also had some tough defeats, such as his 2002 loss to Gov. Ed Rendell in the gubernatorial primary.

"Casey is not a good campaigner. That's why Rendell mopped up the floor with him. He's charisma challenged. He's not as quick witted as Santorum. He doesn't come off as well," Maranto said.

But unlike Santorum, whom former U.S. Rep. Joe Hoeffel, called arrogant, Hoeffel said Casey is "the most decent man I know."

"He's very down to earth. He's very direct. He does not have an overpowering ego," said Hoeffel, a Democrat who considered challenging Santorum.

Pennsylvania, with a mix of urban and rural demographics, has proven a tough state to master politically. There are about 500,000 more registered Democrats than Republicans.

The state has a Democratic governor and went for Democratic candidate John Kerry in the 2004 election, but a majority of its national elected officials are Republican. It has some of the most conservative abortion laws in the country.

Like Santorum, Casey is Catholic. He has four children; Santorum has six. According to a Quinnipiac University poll from July 13, 53 percent of Pennsylvanians said abortion should be legal in either all or most cases.

By selecting a candidate who is against abortion, Santorum does not have an advantage by saying he supports family values, said Randall Miller, professor of history at St. Joseph's University.

"The monopoly that Republicans have been able to claim on some of these issues that seem to mobilize voters over the last several elections, that monopoly does not exist in Pennsylvania with Bob Casey Jr.," Miller said.

But some voters, like retired teacher Ginny Doughery, who are ardently opposed to abortion, remember when Casey's father was not allowed to speak on his anti-abortion views at the party's national conventions in 1992 and 1996. She said Santorum has clout and people listen.

"Even if Casey were elected, he wouldn't have a chance in the Democratic Party of even getting any of his views across," said Doughery, a mother of five. "He wouldn't have any pull at all."