Chris Carlson, Associated Press
Republican presidential candidate, former Pennsylvania Sen. Rick Santorum is surrounded by news media following a campaign appearance at the Indianola Public Library Saturday, Dec. 31, 2011, in Indianola, Iowa.

SIOUX CITY, Iowa — Republican presidential candidate Rick Santorum is telling the conservative activists who pushed his rise in the polls that they can send a message to the world about family and faith by giving him a solid showing in Iowa's leadoff caucuses.

Santorum says his core message is that the strengths of the nation are family and faith. He says that message is increasingly resonating throughout Iowa, particularly in the rural northwest, where his campaign began to catch fire. He spoke Sunday in a Sioux City coffee shop in that was so jammed it was virtually impossible to move.

As Santorum's standing in the polls has increased, some of his rivals have begun attacking him. He says he's ready for that criticism and he's been through tough campaigns before.