Judge Frank Easterbrook pressed prosecutors to explain the difference between bribery and good-old political horse trading, the Chicago Tribune reported.
"If I understand your position, Earl Warren should have gone to prison, Dwight Eisenhower should have gone to prison. ... Can that possibly be right?" Easterbrook asked.
Eisenhower appointed Warren, the governor of California, to the U.S. Supreme Court in 1953 in exchange for his support in the 1952 presidential election.
Easterbrook and two other judges from the 7th U.S. Circuit Court of Appeals will determine Blagojevich's appeal.
Legal analysts told the newspaper the court has a tradition of playing devil's advocate, and Friday's proceedings aren't necessarily a good omen for the defense.
Blagojevich, who was impeached in 2009, was convicted of 18 corruption-related charges -- including trying to sell the U.S. Senate seat of President Barack Obama -- over the course of two trials in 2011 and sentenced to 14 years in prison.
He has been in prison since March 2012 at a minimum-security federal prison near Denver.
On her Facebook page this week, Blagojevich's wife, Patti, urged his supporters to attend the court hearing.
"A show of support would mean a lot to us," she posted.
She appeared in the front row Friday and took notes of the arguments, the Tribune said.
"Here we are again," Patti Blagojevich said. "I just want to say during this holiday season that there isn't a day or moment that goes by that my daughters and I don't feel the emptiness of the absence of my husband. We just hope and pray that he will be home soon with his family."
The appeal raised eight instances in which the defense said U.S. District Judge James Zagel's rulings prevented Blagojevich's attorneys from offering evidence or otherwise deprived Blagojevich of a fair trial.