JANESVILLE -- Republican presidential front-runner Donald Trump, speaking to a crowd of thousands at a rally here Tuesday afternoon, took square aim at Gov. Scott Walker, the GOP executive of the state he hopes to win in next week's April 5 primary.

As protesters and thousands of supporters who couldn't squeeze into the Janesville Convention Center waited outside, Trump told the crowd he is less tied to special interests than his rivals. Trump predicted if he prevails in the Wisconsin primary next week, the GOP race would be "pretty much over."

Earlier in the day, Walker -- a former rival of Trump's for the presidential nomination -- announced he is backing U.S. Sen. Ted Cruz of Texas. Ohio Gov. John Kasich is the other GOP candidate.

At the rally Tuesday afternoon, Trump said Wisconsin's economy isn't performing as many in the state would like. That, he suggested, is partly Walker's fault.

"Am I going to say he's doing a great job? He's not doing a great job," Trump said of Walker.

Speaking earlier Tuesday on a Rockford, Ill., talk radio station, Trump, referring to Walker, boasted that "we sent him packing like a little boy" in the presidential race.

He walked out, frankly, in disgrace. Im surprise hes got any juice left in Wisconsin, Trump said.

Walker's name received a healthy smattering of boos when Trump mentioned it during the rally. Janesville native and U.S. House Speaker Paul Ryan also received some boos when Trump cited him -- a reaction that seemed to surprise Trump.

Unlike some Trump rallies elsewhere, Tuesday's event was largely free of disruptions from protesters inside the venue. A handful of protesters jeered Trump but were quickly escorted out of the Janesville Convention Center without incident.

Outside, protests were largely peaceful though a few anti-Trump protesters clashed with some Trump backers who received tickets for the event but couldn't fit inside the convention center. In one incident, a women punched another person and was pepper-sprayed; she later received medical attention.

Speaking on a Rockford, Ill., talk radio show earlier in the day Tuesday, Trump said he thinks he should do well in the Wisconsin primary. But he lamented that the race here "seems to be a pretty well-stacked deck.

Trump made the round on local conservative talk radio Monday and got a rude welcome. The hosts to which he spoke, several of whom had endorsed Cruz, prodded Trump about his campaign pledges and what they described as his crass rhetoric and inconsistent support for conservative principles.

"Its a pleasure speaking to two people that have an open mind," Trump said later in the interview. "I called three or four people yesterday in Wisconsin that were absolutely ridiculous. I mean the shows were ridiculous -- just so closed."

Trump also took aim at the U.S. military while lamenting his campaign theme that "our country doesnt win anymore."

"Our military cant defeat ISIS," Trump said. "Can you imagine General Patton not being able to defeat ISIS? Hed laugh at ISIS. Hed have ISIS gone in one week.