SCANDAL-PLAGUED GOP SENATOR ANNOUNCES RESIGNATION…. So far in the 112th Congress, the number of Republican lawmakers to resign in disgrace tops the number of major legislative accomplishments, two to zero.

Senator John Ensign of Nevada, the subject of an ethics investigation related to his affair with the wife of a former top aide, announced Thursday evening that he was resigning, effectively ending the high-profile Senate inquiry that had already ruined his once-promising political career. […]

“While I stand behind my firm belief that I have not violated any law, rule, or standard of conduct of the Senate,” he said [in a written statement], “and I have fought to prove this publicly, I will not continue to subject my family, my constituents, or the Senate to any further rounds of investigation, depositions, drawn out proceedings, or especially public hearings. For my family and me, this continued personal cost is simply too great.”

Yes, if there’s one thing John Ensign worries about, it’s putting his family through a difficult ordeal.

To briefly recap for those who’ve forgotten — it’s always irked me that major media outlets almost completely ignored this story — Ensign’s humiliation came to public attention in June 2009, when we learned the conservative, “family-values” senator carried on a lengthy extra-marital relationship with one of his aides, who happened to be married to another one of his aides. Ensign’s parents tried to pay off the mistress’ family.

The scandal grew far worse when we learned that the GOP senator pushed his political and corporate allies to give lobbying contracts to his mistress’s husband. When Douglas and Cynthia Hampton left Ensign’s employ — because, you know, the senator was sleeping with Cynthia — Ensign allegedly took steps to help them make up the lost income, leaning on corporate associates to hire Douglas as a lobbyist, and ignoring ethics laws that restrict how quickly former aides can begin lobbying careers.

Federal investigators ultimately found that Ensign’s wrongdoing didn’t warrant prosecution, but an investigation from the Senate ethics committee, as of last month, appeared to be intensifying. By resigning in disgrace, Ensign is cutting that probe short, though committee members may yet issue a report, and refer the matter to the Justice Department if they uncover evidence of criminal wrongdoing.

As for the electoral implications, Nevada’s Republican governor, Brian Sandoval, will appoint Ensign’s replacement to serve through next year. It’s generally assumed Sandoval will tap Rep. Dean Heller (R), who’s running for the seat anyway, and would be able to run as a quasi-incumbent, while avoiding controversial votes in the House that would be used against him (Heller voted last week, for example, to eliminate Medicare). There would, under this scenario, also be a special election in Heller’s Nevada district, which would quickly become a hotly contested race.

Ensign’s resignation, which is effective May 3, marks the end of what was once a promising career. Indeed, before the scandal, it was widely assumed that Ensign would run for president in 2012, and was considered a credible candidate. Now, however, the far-right senator leaves in disgrace, unable to overcome his personal and professional misconduct.

Somewhere, Sen. David Vitter (R-La.), who easily won re-election after getting caught with prostitutes, is laughing his ass off.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.