He declared war.
War with the public union bosses, war with Boss Madigan, even with some Republicans who he says have been co-opted by the corrupt Springfield status quo.
Rauner ticked off an optimistic pro-growth, pro-education and pro-jobs agenda. He announced he'd push for term limits so that if elected governor, he would be able to fire himself in eight years.
And he addressed that $100 billion public pension deficit strangling the state. For decades the politicians of both parties have done nothing about it, while currying union favor, votes and campaign cash.
"I've got news for you," he told me, sitting for an interview on my WLS-AM radio program, "I am officially today, as of 20 minutes ago, running for governor of Illinois. And I'm excited and honored by the opportunity to go to work for you guys and every person in Illinois.
"We've got to turn our state around. We've got to shake up Springfield. We've got to bring back our state, and I'm excited and honored to lead that effort," he said.
As I told you months ago in this column when he first went public with his political plans, Rauner doesn't scare easy. He made too much money as a venture capitalist to be scared off by tough guys. And he says he's not worried about the state's political class, or by the powerful public worker unions like SEIU and AFSCME that dominate the Democratic Party here run by Boss Madigan.
But can he take what's coming to him?
"Sure I can," Rauner told me during a break.
I'm not so certain. Rauner hasn't gone through that bloody gantlet of reporters and opposition researchers tearing through his life. No one who hasn't experienced it can say for certain they can handle it.
I'm not condemning the process. It is what it is. A man or woman who wants to run a state, or a country, and shape lives and wield the awesome power of government better understand that this is necessary.
But for all that media love, Obama never had the guts to challenge the Illinois status quo. And Rauner has made enemies.
He's called out House Speaker Michael Madigan and the public unions. They have friends and allies in the courts, among lawyers, in business, everywhere Rauner has been.
So can he take having his divorce records pored over by opposition research experts, and meaty bits of information handed to reporters just waiting for the rich guy to explode?
Can Republican Rauner handle questions about his huge campaign contributions to Democrat and former Mayor Richard M. Daley? And questions about whether Rauner clouted his own child into a magnet school?
Will he blow his cork? Or will he smile and stay on message?
We don't know. Not yet.
But what I saw of the man on Wednesday was impressive enough. Rauner targeted Madigan, the chairman of the Illinois Democratic Party, and the boss' daughter, Illinois Attorney General Lisa Madigan.
He said that "it would be terrible" for Illinois if Boss Madigan installed his daughter in the governor's mansion.
"I firmly hope and believe that voters in Illinois would never tolerate that," Rauner said. "And I would aggressively run against that. That would be terrible for us. I don't want to talk about any specific person today, as a candidate or potential candidate. What I want to change — and I'm on a mission to do it — is change the culture and inside dealing and the perpetuation of that structure in Springfield. And more of that (Madigan) family, more of the existing career politicians, is status quo and that's killing us."
I also asked him about the possible gubernatorial candidacy of former White House chief of staff Bill Daley, the son of a legendary mayor, the brother of a troubled mayor.
Bill Daley has experience and money and can raise more cash. He has the connections and business knowledge to make himself governor, and the temperament to actually run the office. Daley is expected to make a decision within days.
Rauner said he's known Bill Daley "a long time. I have no idea whether Bill is going to run or not. And I haven't spent any time worrying about who is going to run and no matter what, I will run against anybody and I will give them the fight of their life. That's for sure.
"What I would be troubled by if Bill ran, is, you know, Chicago has a culture, and Bill's part of it," Rauner said. "It's a machine. It's an operation. Government unions are a big part of it. And we can't have that culture even more transported down to Springfield than it already is."
Meet us at Lit Fest: Would you like to know the deep secrets of how this column comes together every day? Meet me and my editor, Mark Jacob, at the Printers Row Lit Fest on Sunday at 10 a.m. at Center Stage. We'll talk politics, food, sports, newspapering, radio, whatever you wish. It's free. And we might even teach you how to do the Moutza.