CHICAGO - Former Illinois Gov. Rod Blagojevich fielded a question on the witnesses stand Wednesday about his most infamous comment of all those captured on FBI wiretap recordings at the center of his corruption trial.

And when he did - he fumbled to explain it.

"I'm afraid to answer this, but I'm not quite sure how to answer it," he said, pausing.

Blagojevich is heard on the 2008 recording speaking excitedly about his power to name someone to President Obama's soon-to-be vacated Senate seat, saying, "I've got this thing and it's f- golden" and "I'm just not giving it up for . . . nothing."

Prosecutors used the excerpt to try to show that Blagojevich sought to sell or trade an appointment to Obama's old seat for a top job or campaign cash. The recording has been widely parodied, and on the stand Wednesday, Blagojevich himself called it "that phrase heard around the world."

"I was saying this opportunity is f- golden. That's what I was saying," Blagojevich started to explain to jurors. After a pause, he continued: "I knew it was a unique opportunity."

It was a rare case in which Blagojevich seemed unsure of himself. He had said more confidently earlier in the day that the opportunity was more to benefit Illinois residents - possibly by helping woo more federal money to the state - rather than a benefit for himself.

Patience seemed to be running thin on all sides Wednesday, Blagojevich's fourth day on the stand.

An angry judge chastised the ousted governor for "smuggling" testimony into the trial that had previously been ruled inadmissible.

Judge James Zagel said Blagojevich had kept bringing up issues or opinions that the judge had ruled shouldn't be mentioned in front of the jury.

Zagel, who sent the jury out of the room before admonishing Blagojevich, implied that the former governor's motives were less than pure.

"I make a ruling, and then the ruling is disregarded, and then I have to say, 'Don't do it,' " Zagel said. "And when you do that more than once or twice, it is inevitable that I'm going to believe that there is some purpose other than the pursuit of truth."