U.S. Senator Tom Coburn (R-Okla.) (KEVIN LAMARQUE/REUTERS)

The ethics committee admonished Sen. Tom Coburn (R-Okla.) Friday for assisting a former Senate aide who was prohibited from lobbying for a period, ending the panel’s three-year investigation into the affairs of former senator John Ensign.

Coburn, once a close friend of Ensign’s, tried to help the Nevada senator throughout 2008 as Ensign’s affair with the wife of a senior staffer threatened to unravel the once-rising star’s career. At one point Coburn, a hero to conservative activists, tried to help Ensign reach a financial settlement with Doug Hampton, who was Ensign’s best friend and served as his administrative assistant until the senator’s affair with Hampton’s wife became known.

The ethics panel focused its “qualified admonition” on Coburn for his role in helping Hampton’s work as a lobbyist during the one-year period after leaving Ensign’s office, when he was still legally forbidden from lobbying the Senate.

“Your communications with and actions on behalf of Doug Hampton were improper conduct which reflects on the Senate,” the six-member committee, made up of three Democrats and three Republicans, said in their letter to Coburn. Their decision to admonish him was unanimous.

The committee also issued an admonition to Bret Bernhardt, chief of staff for Sen. Jim DeMint (R-S.C.), who helped set up a meeting for Hampton with DeMint at a time when Bernhardt knew Hampton was forbidden from lobbying.

Former Sen. John Ensign of Nevada (AP)

An admonition is a lower form of punishment from the ethics committee, requiring no formal vote by the full Senate and no fine or other punishment.

Coburn defended his action by saying that the “burden of compliance” with the law rests with the staffer-turned-lobbyist, not with the staff and lawmakers who do not know the precise timing of when some former aide’s “cooling off” period ends.

“Admonishing Dr. Coburn for failing to know Hampton was only seven weeks shy of ending his year-long cooling off period is gratuitous, particularly when Dr. Coburn cooperated fully with the ethics committee and went out of his way to acknowledge that he could have taken additional steps to learn that Hampton was under the ban,” John Hart, Coburn’s spokesman, said in a statement.

The new punishments from the ethics committee come a year Ensign resigned rather than testify under oath about his dealings with Hampton. Nine days after he formally left the Senate, the committee’s top Democrat and Republican, Sens. Barbara Boxer (Calif.) and Johnny Isakson (Ga.), unveiled a report suggesting that Ensign engaged in a vast conspiracy to financially provide support for Hampton to keep him from going public with the affair.

“We have reason to believe Senator Ensign violated laws,” Boxer said at the time, as the panel forwarded its reports to the Justice Department.

Hampton is expected to plead guilty next month to violating federal lobbying laws as part of Justice’s ongoing investigation. It’s unclear whether that will close the criminal probe or whether federal investigators will try to focus on Ensign’s assistance to Hampton.

In the spring of 2008 Coburn was part of a collection of friends to whom Hampton reached out in order to force Ensign to end his affair with Cynthia Hampton, whose close friendship with Ensign’s wife, Darlene, brought the two families together. They shared holidays together, vacationed together, moved into the same neighborhood outside Las Vegas. Finally, Ensign persuaded Doug Hampton to move to Washington to serve on his legislative staff while putting Cynthia Hampton on his political payroll as his treasurer.

After prodding from Coburn and his friends, Ensign ended the affair and fired both Hamptons from his staff. Ensign’s parents wrote $96,000 worth of checks to the Hampton family, and then Ensign began helping Doug Hampton advance his lobbying career even though federal laws forbid former staffers from lobbying the Senate for a full year after leaving Capitol Hill.

Ensign helped Hampton receive a job with a Nevada-based firm and assisted him in getting clients, including a Nevada airline. In March 2009 Hampton had meetings with Coburn and then DeMint on the same day, during which he pressed the senators for help on legislative matters related to the airline, according to the ethics committee.

The investigation found that no action was taken on behalf of Hampton or his clients, but that both Coburn and DeMint’s chief of staff knew that he was not allowed to be lobbying the Senate at that time.