By Jay Levine

(CBS) — There’s potential trouble for Congressman Bobby Rush as thousands of signatures on his nominating petitions are being challenged.

CBS 2’s Chief Correspondent Jay Levine explains.

He is 69 years old and the Dean of Illinois Congressmen, a fixture on South Side; former Black Panther, activist and alderman. But now, according to challenger Howard Brookins, he’s past his prime.

“For too long our congressman has been absent,” Alderman Brookins said. “Not in Washington, not in the district.

Bobby Rush has beaten cancer, an ethics investigation — so far — and criticism he’s done too little to stop the escalating violence in his district.

But time is short. Thursday in Springfield, lawyers for Alderman Brookins, who have challenged more than 2,300 of Rush’s 3,100 signatures on nominating petitions, will try to get Rush tossed off the March primary ballot.

Brookins’ attorney Mike Dorf says the chances are, “well better than 50 percent.”

Congressman Rush was in Washington Wednesday. He declined our request for an interview; refusing to make any comment at all. But his attorney Brendan Schiller blasted the challenge and challenger.

“This is a frivolous challenge that was a way to get free media,” he said. “It’s a cheap ploy.”

Schiller contends that signatures that Brookins’ attorney claims were written by the same person, are clearly legitimate.

“All but two of their duplicate signature challenges were completely frivolous,” Schiller said. “They’re obviously not duplicate signatures.”

But Brookins says these and other challenges will stand, and that Rush’s petition problems are an indication it’s time for him to go.

“I think it is a symptom of also not keeping your eye on the ball, like he hasn’t been keeping his eye on the district,” Brookins said.

Examiners will spend all day Thursday examining signatures of those allegedly not registered to vote, living outside the district, or not at addresses they’ve listed. By late Thursday evening, we should have a pretty good idea of if Rush’s biggest re-election obstacle are his own petitions.

A formal and final decision by the State Board of Elections, on whether the challenges are enough to keep Rush off the march primary ballot, won’t be made until January.