NEW YORK (CBSNewYork) — A fourth day Tuesday on the witness stand for a real estate developer who accuses Mayor Bill de Blasio of taking part in pay-to-play politics.

The mayor has defended himself against the testimony of one of his biggest campaign donors, Jona Rechnitz, that he was part of an alleged pay-to-play scheme at City Hall.

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“He’s a liar and a felon and that’s all you need to know,” de Blasio said. “I’ve covered this very clearly. He’s said things that aren’t true about me.”

On his third day testifying in the bribery trial of former corrections union boss Norman Seabrook, Rechnitz again talked about his weekly contact with de Blasio, through email, texts, phone calls and communication through the mayor’s Campaign Finance Director Ross Offinger.

In court, Rechnitz admitted to gifting Offinger with paid hotel accommodations for a vacation in the Dominican Republic.

When pressed by CBS2’s Marcia Kramer, the mayor tried to steer attention back to his campaign, making an appearance with Bernie Sanders and getting the endorsement of Sen. Charles Schumer, who was asked if he ever reconsidered his support of the mayor given the corruption allegations.

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“Far and away, the two most important criteria in endorsing a mayor is crime is down, jobs are up,” Schumer said.

But the mayor’s opponents in next week’s election have been quick to call for a further investigation into Rechnitz’s claims.

“This mayor has continued to play New Yorkers for fools,” Nicole Malliotakis said.

“This witness was credible enough for the U.S. Attorney’s Office,” said Bo Dietl. “What he’s saying in the courtroom right now is pay to play.”

In March, Rechnitz pleaded guilty to donating money to government officials in exchange for favors.

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Rechnitz admitted Monday to withholding the truth during interrogations by federal investigators until he was offered leniency in his sentencing in exchange for his testimony in the Seabrook trial.