Federal investigators have issued subpoenas to the National Republican Senatorial Committee for documents relating to Sen. John Ensign’s (R-Nev.) tenure there, the committee confirmed Thursday.

The subpoenas, part of a widening investigation by federal authorities into Ensign, come at a bad time for Senate Republicans, who want to focus their energies on defeating Democrats’ health care legislation.

“It is a distraction … but there’s not much more [Senate Minority Leader Mitch McConnell (R-Ky.)] can do,” a senior GOP aide said, noting that the GOP leadership has no way to force Ensign out of office.

According to Republicans, current NRSC Chairman John Cornyn (Texas) — a former member of the Ethics Committee — is cooperating with federal officials.

“The NRSC has responded appropriately to questions concerning matters related to the 2008 election cycle time frame,” NRSC General Counsel Sean Cairncross said. No current employees of the NRSC have been asked to testify, and the inquiry has been limited to Ensign’s time at the committee, a Republican familiar with the situation said.

The FBI and Senate Ethics Committee are separately investigating Ensign’s efforts to cover up an affair with a campaign aide who also was married to his top personal office aide. Citizens for Responsibility and Ethics in Washington and others have accused Ensign of using his office to steer business toward the lobbying business of Doug Hampton, a former aide who is married to Ensign’s ex-mistress, Cynthia.

On Wednesday it was reported that a number of Las Vegas-based businesses had also been subpoenaed as part of the investigation.

“Sen. Ensign is confident he has complied with all ethics rules and laws and will cooperate with any official inquiries,” Rebecca Fisher, spokeswoman for Ensign, said Thursday.

Jessica Brady contributed to this report.