New Jersey Gov. Jim McGreevey's top campaign contributor pleaded guilty in federal court on Wednesday to 18 charges related to an alleged blackmail plot.

Charles Kushner (search), a real-estate mogul, pleaded to charges, including witness retaliation, tax evasion and violation of election laws.

One charge alleged that Kushner attempted to intimidate a witness in a federal investigation.

The charge stated Kushner hired a prostitute to have sex with his own brother-in-law, who was testifying against him, and then mailed a video of the tryst to his own sister. However, the plot failed when Kushner's sister and her husband notified authorities instead of keeping silent.

According to the terms of his plea bargain, Kushner faces no more than two years in prison. Had he been convicted at trial, he could have gotten 10 years. Sentencing will take place on Nov. 29.

The plea deal was "non-cooperative," meaning Kushner gives up little information to authorities regarding influence-peddling in New Jsersey by other McGreevey associates.

Kushner is also notable for sponsoring a work visa for Golan Cipel (search), the Israeli man with whom McGreevey allegedly had an adulterous affair, and who has threatened to sue McGreevey for sexual harassment and sexual assault.

Kushner attorney Ben Brafman said after the guilty plea that Kushner signed the visa for Cipel five years ago "and has not talked to him in years."

Cipel, 35, served briefly as New Jersey's homeland security adviser in 2002. After it was discovered he had never had a background check, and that no official announcement of his appointment had ever been made, Cipel was reassigned.

Soon afterward, he left government for a private-sector job in New York.

McGreevey, 47, resigned as governor last Thursday after announcing that he was gay and had had an affair with an unnamed man, who sources quickly identified as Cipel.

Cipel was said to have demanded millions of dollars to stay quiet about the affair, but within days of McGreevey's resignation, he told an Israeli newspaper that he was not gay and that the governor, his former boss, had repeatedly made unwanted sexual advances.

The claim was denied by McGreevey's aides.

McGreevey had no public appearances scheduled for Wednesday, a spokesman said, though he was expected to be at the Statehouse in Trenton for routine meetings with advisers.

U.S. Attorney Christopher J. Christie said he was investigating the possibility of criminal wrongdoing as a result of the extramarital affair, but would not specify whether his office was looking more into McGreevey's alleged misconduct or into Cipel's alleged extortion attempt.

On Wednesday, the New York Daily News reported that a male college professor from northern New Jersey had claimed to have had a romantic relationship with Cipel, who by Tuesday had returned to Israel.

The mystery man's story, if true, would lend credence to allegations that Cipel was trying to shake down McGreevey.

According to the Daily News, the professor had notified McGreevey's office of his relationship with Cipel. In turn, the governor's office apparently had hired a private investigator to look into the man's claims.

Cipel refused to elaborate on the widening scandal Tuesday, but said he expected to return to the United States within a few weeks.

As the scandal grows, so does speculation that McGreevey could step down before his self-imposed Nov. 15 resignation date. That would make possible a special election to fill out his term, which ends in January 2006.

If the governor stays on until Nov. 15, the state Senate president will finish out McGreevey's term.

Some Democratic power brokers want an earlier exit for McGreevey, and were reportedly meeting behind closed doors to urge U.S. Sen. Jon Corzine (search) to run for governor.

However, Corzine is the chairman of the Democratic Senatorial Campaign Committee and is intent on ensuring as many Democrats as possible are elected to the Senate next year.

Corzine's spokesman David Wald said, "Jon continues not to be among those pushing for a special election."

Republicans are also calling for McGreevey to step aside sooner than later. On Tuesday, former Gov. Christine Todd Whitman (search) urged McGreevey to listen to his conscience and quit now.

Whitman denied any interest in running for governor again herself. Other Republicans said they might try to recruit former Gov. Tom Kean (search), currently chairman of the Sept. 11 commission.

Kean also said he was not interested.

"I'm doing this now, not that," Kean said after a hearing before the House Homeland Security Committee in Washington.

Fox News' David Lee Miller and the Associated Press contributed to this report.