Rick Santorum, the boyish-looking 47-year-old senator from Pennsylvania, could not, in more decorous political times, have risen to a position of much power in Congress. He has been impatient and sometimes impertinent -- the political equivalent of the too-rough kid on the playground who either doesn't know the rules of the game or just doesn't care to follow them. In the House in the early 1990's, he fell in with a band of junior Republicans (nicknamed the Gang of Seven) who pushed aggressive investigations of both Democrats and Republicans. Elected to the more mannered Senate in 1994, Santorum took to the floor just months into his tenure displaying a sign for several days that read ''Where's Bill?'' to spotlight what he perceived as President Clinton's lack of leadership on balancing the federal budget. (Senator Robert Byrd, Democrat of West Virginia, commented that the young senator's style seemed more appropriate for ''an alehouse or beer tavern.'') In a much-publicized interview in 2003, he argued that the Supreme Court should not overturn state sodomy laws that ban homosexual sex and suggested that such a ruling would create a justification for bigamy, polygamy and incest. At one point, he even raised the specter of bestiality, using the phrase ''man on dog.''

Santorum has not so much accommodated himself to Washington as the city, stylistically and politically, has moved in his direction. He became chairman of the Senate Republican Conference in 2000, his party's third-ranking leadership position. If he wins a third Senate term in 2006, he will most likely move up to Republican whip, the No. 2 spot. His influence already exceeds his rank. At a time when overt expressions of religiosity are increasingly a part of politics, Santorum is, with the exception of President Bush, the nation's pre-eminent faith-based politician -- a devout Catholic so valued by religious conservatives of all faiths that Time magazine recently included him on its list of America...