At a press conference today, Gov. Pat Quinn said that the Democrats' lieutenant governor nominee  "has a lot of explaining to do ... about very serious matters," referring to revelations regarding Scott Lee Cohen's 2005 arrest on domestic violence charges.

Quinn said: "I think it's important that anyone who's been in an election ... if there are questions raised about their conduct after the election, they have to come before the public, in the arena, and answer any and all questions about their conduct.  And if those questions aren't properly answered, they have to take the appropriate steps."

Quinn also denied allegations that he had been "warned" by State Sen. Terry Link about Cohen's history.  "The first time I heard about it was yesterday morning," he said. "No one on my campaign staff told me about it. ... I had no idea about these matters."

He continued: "If there are matters raised about your conduct that disqualify you from running a proper way for an election in the fall, then the only appropriate thing is to step aside.  And I think that's what we're looking at here.  I do think that somebody who has had these matters raised about their conduct should have a chance to speak in the public arena.  But if their explanations are unsatisfactory, if their conduct is not appropriate, the only way to go is to step aside."

UPDATE (2:05 p.m.): Here is Cohen's response, via WBEZ:

"I have no intention of stepping down or stepping aside. When the facts come to light, after my ex-wife and ex-girlfriend speak, the people of Illinois can decide, and I will listen to them directly. I am asking my ex-wife and ex-girlfriend to come forward and to talk with the media. There are questions, and I will provide all answers honestly and openly. I only ask for time to do the interviews. 2005 was a difficult time in my life. I was going through a divorce, and I started running with a fast group. I was in a tumultuous relationship with the woman I was dating. We had a fight, but I never touched her. She called the police, however, she never came to court, and the charges were dismissed. I realized this relationship was not healthy, I ended it, and we parted amicably."