CHICAGO (AP) — A lawyer for former U.S. Rep. Aaron Schock told a federal appeals court in Chicago Wednesday that federal prosecutors are aiming to become the first — with the court's help — to imprison a former member of Congress based on "ambiguous" rules the U.S. House set for itself.

Schock's lawyer argued the point during a 45-minute hearing before a three-judge panel of the 7th U.S. Circuit Court of Appeals, which is mulling Schock's request to have all 22 charges left in his corruption case tossed before it ever gets to trial.

A key question facing the court is whether prosecution of the 36-year-old Peoria Republican for allegedly misusing government and campaign funds violates separation-of-powers and other clauses in the U.S. Constitution.

Defense lawyer Benjamin Hatch said the U.S. attorney office in central Illinois "would have this court be the first in the nation to hold that a member of Congress can be sent to prison based on ambiguous or debatable interpretation of House rules."

Once seen as a rising star in the GOP, Schock gained notoriety for redecorating his Capitol Hill office in the style of the "Downton Abbey" TV series. He resigned in 2015 as scrutiny of his spending intensified.

Several courts have agreed the Constitution bars prosecutors, as members of the executive branch, from charging legislative-branch members based on unclear congressional rules. They can be charged based on clear rules that require no interpretation, courts have also found.

Schock's lawyers have argued that all the charges derive, directly or indirectly, from imprecise rules. They singled out one that relied on alleged fraudulent reimbursement for a $5,000 office chandelier. The rule prohibits reimbursements for "decorations" and "furniture", the appeal said, but doesn't define either word.

Prosecutors said half of the charges Schock faces have nothing to do with House rules, including ones alleging he falsified tax returns.

A Department of Justice lawyer, William Glaser, said at Wednesday's hearing that the defense was mischaracterizing the government's approach — as if "we want to go around prosecuting people based on ambiguous rules."

Glaser said prosecutors won't rely heavily on House rules in trying to prove their case at a trial for Schock. In some instances, he said, showing Schock violated rules would simply be a way to try and show criminal intent.

"We would prefer to have this case about his underlying conduct and not primarily about particular ambiguities in rules," he said.

One of the judges on the panel, Diane Wood, responded: "That's a sound approach."

She added Schock has a right not to be prosecuted based on especially vague rules. The furniture rule, she said, seemed vague to her. She said other rules, like ones regarding reimbursements for the use of private cars on congressional business, seemed straight-forward.

Schock made a rare public appearance by attending the hearing but declined to comment as he left. A spokesman did release a statement from him.

"It was obvious from day one that this prosecution was convinced of one thing: they needed to find something, anything to prosecute me," Schock said in the statement.

Judges Wednesday directed their toughest questions to Schock's lawyer, but none gave a clear sense of how they are leaning.

The panel includes two judges appointed by a Republican president — Ronald Reagan — and one appointed by a Democrat — Bill Clinton.