"Don't settle for what's not good enough to save the country," the newly ascendant Santorum implored Iowans at City Hall in Coralville, urging voters to put conservative principles above everything else and suggesting that his rivals, and specifically Texas Rep. Ron Paul, lacked them.
For the first time, though, the former Pennsylvania senator became a target.
"When he talks about fiscal conservatism, every now and then it leaves me scratching my head because he was a prolific earmarker," Perry, the Texas governor, said of Santorum as the day began. He was referring to special spending projects members of Congress seek. "He loaded up his bill with Pennsylvania pork."
Perry also slapped at Santorum in a radio ad and in a new TV commercial that lumps him in with Minnesota Rep. Michele Bachmann, former House Speaker Newt Gingrich and Paul and says: "The fox guarding the henhouse is like asking a congressman to fix Washington: Bad idea."
The maneuvering underscored the fluid -- if not convoluted -- state of the GOP presidential race. As Tuesday's caucuses loom, cultural conservatives and evangelical Republicans, who make up the base of the electorate here, continue to be divided.
That lack of unity paves the way for someone who is seen as less consistently conservative.
Five days out, public and private polling show Romney and Paul in strong contention to win the caucuses, with coalitions of support cobbled together from across the Republican political spectrum and their get-out-the-vote operations -- beefed up from their failed 2008 bids -- at the ready. They're the only two with the money and the organizations necessary to ensure big turnouts on Tuesday.
Santorum, Perry and Gingrich will have to rely largely on momentum to carry supporters to precinct caucuses. Each was working to convince fickle conservatives that he alone would satisfy those who yearn for a nominee who would adhere strictly to GOP orthodoxy.
Bachmann, meanwhile, worked to convince backers that her cash-strapped campaign was not in disarray after her Iowa campaign chairman, state Sen. Kent Sorenson, abandoned her to back Paul.