CHICAGO — Prosecutors at Rod Blagojevich’s corruption retrial kept hammering Thursday at the highest-profile allegation against the former Illinois governor, playing wiretap recordings of Blagojevich that they say shows he tried to trade or sell President Barack Obama’s vacated U.S. Senate seat.

Most of the FBI recordings played Thursday were of conversations between Blagojevich and his chief of staff, John Harris, in the weeks after Obama won the presidential election in November 2008. Harris, who is testifying under a plea deal, was on the stand for a third day testifying about the recordings.

Prosecutors finished questioning Harris on Thursday afternoon, and the judge adjourned until Monday after the defense said the lawyer designated to cross-examine Harris, lead attorney Aaron Goldstein, was ill and had gone home.

In the recordings played to jurors on Thursday, the giddiness Blagojevich seemed to exude in early November about the prospect of benefiting from Obama’s victory started to dissipate, and he sounds increasingly frantic about landing a top-salary job.

“It’s very important for me to make a lot of money,” he says bluntly in a Nov. 12, 2008, phone conversation with Harris.

Part of his motivation, he tells Harris, is fear for the future of his wife and two daughters.

“How the hell am I gonna send my kid to college,” Blagojevich says about his worsening finances and legal scrutiny of his administration. “Never again am I ever gonna (bleepin’) screw my kids and my family. . . . I gotta fix this.”

Blagojevich, 54, faces 20 charges at this retrial. His initial trial ended last year with jurors deadlocked on all but one charge — convicting Blagojevich of lying to the FBI.

In recordings played Thursday, Blagojevich seems to indicate he now knows Obama isn’t willing to cut a deal on the Senate seat. But he also believes the White House has a dilemma: They don’t want him to appoint himself to the seat and bring his associations to Chicago corruption with him to Washington.

Blagojevich singles out convicted political fixer Tony Rezko, who did fundraising for both Blagojevich and Obama. After his 2008 conviction, Rezko quickly became a byword for pay-to-play politics in Illinois.

By December, Blagojevich also understood that Obama’s friend Valerie Jarrett no longer wanted the seat, so he couldn’t use her as leverage to try to secure an administration job, Harris told jurors.

Prosecutors briefly touched Thursday on other allegations, including that Blagojevich tried to squeeze a racetrack executive for campaign cash. But they later turned back to the Senate seat.

By zeroing in on that allegation first, prosecutors appear to be addressing criticism after the first trial that they delivered a case that was too scattershot and difficult for jurors to follow.