WASHINGTON — Sen. Robert Menendez, who federal prosecutors say used his office to benefit a wealthy donor, has been accused of ethical improprieties before. But none of those accusations has led to findings of misconduct.

“Whenever these things have come up, he’s gone on the offensive, managed to blunt or discredit the accusations or simply ride out the storm,” said Ross Baker, a Rutgers University political science professor.

In 2006, the New Jersey Democrat was investigated for accepting rent from a nonprofit — the North Hudson Community Action Corp. — while helping the group seek federal funding as a U.S. House member. Menendez sold the building in 2003 after collecting more than $300,000 in rent.

At the time of the investigation, he was serving in the Senate by appointment — former senator Jon Corzine named Menendez to replace him in January 2006 after becoming New Jersey’s governor — and was running for election to a full term against state Sen. Tom Kean Jr.

The investigation was launched by then-U.S. attorney Chris Christie. It was closed in 2011 without charges after Christie became governor.

Also in 2006, Republican state lawmakers in New Jersey filed a complaint with the U.S. Senate Ethics Committee alleging that Menendez, while a U.S. House member, lobbied unsuccessfully in 2002 against the merger of two Spanish-language broadcasting stations while holding stock in a competing company.

In 2003, he also introduced legislation, never enacted, to make it harder for such companies to merge. Employees at the competing company, Spanish Broadcasting System, had contributed to Menendez’s campaigns.

Menendez said his investment was unrelated to his position against the merger, which he said would be bad for consumers. He told The Star Ledger of Newark, N.J., at the time that he “did nothing for the North Hudson Community Action Corp. that was inappropriate or unethical.”

He blamed both sets of allegations on smear tactics by the Kean campaign.

“(Kean) ultimately intends to try to drive this election through the politics of personal destruction,” Menendez said at the time.

After winning the 2006 Senate election, Menendez faced other challenges. He spent $150,000 in legal fees fending off a Tea Party-led effort to force his recall in 2010, according to a report filed with the Senate Office of Public Records.

Salomon Melgen, the wealthy donor at the center of the current federal case against Menendez, was a top contributor to the legal defense fund. He and his and his wife, Flor, donated a total $40,000 in 2011 and 2012.

Raul Alarcon, CEO of Spanish Broadcasting System, donated $10,000.

A more recent defense fund related to Menendez’s current legal problems spent $762,576.96 last year.

“When you look at Sen. Menendez’s history, he’s obviously weathered many, may accusations and his record on persevering through them is perfect,” said Jersey City Mayor Steven Fulop, a Democrat who ran unsuccessfully for Congress against Menendez in 2004.

Contributing: Associated Press