FRANKSVILLE, Wis. (AP) -- An agitated Rick Santorum on Sunday called Mitt Romney "the worst Republican in the country to put up against Barack Obama" even as it appears the former Massachusetts governor is on pace to clinch the party's nomination in June.
Santorum later lashed out at reporters, using a profane word as he accused them of "distorting" his speech.
Santorum told voters that Romney is "uniquely disqualified" to be the GOP's presidential pick and urged his supporters to stand with him even as he faces an increasingly improbable pathway to the nomination. Santorum said "the race isn't over until the people of Wisconsin sing," and urged them to give his underfunded, underdog campaign a chance to derail Romney.
"Pick any other Republican in the country. He is the worst Republican in the country to put up against Barack Obama," Santorum said at an evening rally near Racine.
Santorum later tried to clarify that he was talking only about Romney's ability to campaign against the national health care law championed by Obama and the Democrats. But the candidate's temper flared when he was pushed by reporters.
"On the issue of health care. That's what I was talking about, and I was very clear about talking about that. OK?" Santorum told reporters who asked him about the scathing criticism. "Come on, guys, don't do this. I mean, you guys are incredible. I was talking about Obamacare, and he is the worst because he was the author of Romneycare."
Pressed by a reporter from The New York Times, Santorum said: "Quit distorting my words. It's bulls---."
Romney spokesman Ryan Williams, who attended the event, said Santorum was "panicking in the final stages of his campaign."
"Rick Santorum is becoming more desperate and angry and unhinged every day," Williams said. "He sees conservatives coalescing around Mitt Romney and he's rattled by the backlash caused by his suggestion that keeping Barack Obama would be better than electing a Republican."
Campaigning throughout Wisconsin, which has its primary April 3, Santorum hammered Romney as a candidate conservatives should not trust. He seized on a Romney adviser's comment last week that the race's dynamic will change when the GOP settles on a nominee, likening it to an Etch A Sketch toy.
"I have not written my public policy pronouncements on an Etch A Sketch. They are written on my heart," Santorum said in a Fond du Lac bowling alley.
"Gov. Romney has said in response to the Etch A Sketch comment that he wants to assure all of you -- he wants to assure that he will run as a conservative in the fall. Let me assure you, that I'm not going to run as a conservative. I am a conservative."
Santorum also called Romney "the one Republican in America who actually authored the blueprint for Obamacare."
"We have a candidate who is running against me who is uniquely disqualified," he said.
But that candidate is better organized and has a serious advantage on his way to clinching the GOP nomination with 1,144 delegates before the party meets for its convention in Tampa, Fla. Romney has won 568 delegates to Santorum's 273, according to The Associated Press' tally.
Santorum would need 74 percent of the remaining delegates to clinch the nomination before the national convention in August, and he acknowledges he is unlikely to keep pace with Romney in spending.
"I can't outspend him in Wisconsin. No way," Santorum told supporters here. "But you can outwork him. We can do this."
Santorum's web site says he has scheduled two appearances for southern Wisconsin on Tuesday.
He was to appear at 11:30 a.m. at the Elks Lodge in Beaver Dam, then at The Armory in Janesville at 6:00 p.m.