Nevada Republican Sen. John Ensign is expected to resign from office in the near future. (AP Photo/Las Vegas Review-Journal, Jessica Ebelhar)

“While I stand behind my firm belief that I have not violated any law, rule, or standard of conduct of the Senate, 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,” Ensign said in a statement posted on his website. “For my family and me, this continued personal cost is simply too great.”

Ensign’s resignation, which was first reported by Las Vegas Sun columnist Jon Ralston, will be official on May 3 and comes six weeks after he announced his plans to retire at the end of his current term, which expires in 2012.

His departure comes as the Senate ethics committee is conducting an ongoing investigation into his handling of an affair with a former political aide -- whose husband was also a top legislative aide to the senator.

Earlier this year the committee hired an outside counsel to begin a more formal investigative phase of Ensign’s actions, which would have likely led to either a public hearing on formal allegations or the public issuing of its allegations against the senator.

Removed from the Senate, the ethics committee has no jurisdiction in the matter and likely will keep private the results of its 20-month investigation.

In June 2009 Ensign publicly admitted that he had an affair with Cynthia Hampton, who was his political treasurer and was married to Doug Hampton, Ensign’s administrative assistant. The Ensign and Hampton families lived in the same neighborhood outside Las Vegas and were considered the best of friends.

In 2008, when the affair became known to the other spouses, Ensign dismissed both Hamptons from his political and legislative payroll. Ensign’s parents, wealthy casino magnates, paid the Hampton family $96,000 in what was labeled gift income for tax purposes, the precise amount legally permissible without triggering taxes.

In addition, Doug Hampton returned to Las Vegas and began working as a lobbyist for a consulting firm run by Ensign’s top political advisers. Doug Hampton has alleged that Ensign helped him line up his first few lobbying clients -- all donors to Ensign’s political committees -- and that the senator helped arrange meetings for Doug Hampton with Obama administration officials.

A Justice Department investigation into possible criminal activity by Ensign ended with no charges. Hampton, however, has been indicted.

Ensign’s resignation will allow newly elected Gov. Brian Sandoval (R) to appoint an interim replacement until the 2012 election next November.

Rep. Dean Heller, a Republican who is running to succeed Ensign, is the clear frontrunner for the appointment and would almost certainly benefit politically from spending the next year as the incumbent senator from the Silver State.

Democrats are likely to face a primary with Rep. Shelley Berkley and wealthy businessman Byron Georgiou both in the race.

If Heller is named to the Senate, there will be a special election to replace him in the sprawling 2nd district, which takes in much of the northern, rural counties of the state.

Sandoval would have seven days from the time he appointed someone to declare a vacancy in the 2nd district. The special election must be held within 180 days of that declaration.

Sharron Angle, the 2010 Senate nominee against Harry Reid, would likely be considered the early favorite in a special election scenario given her high name identification and fundraising prowess.

Democrats believe Angle’s divisiveness with a general election electorate could create a pickup opportunity in the state. No Democrat has formally announced plans to run although Secretary of State Kate Marshall is mentioned.

The district went for Sen. John McCain (R) by fewer than 100 votes in 2008.

Ensign’s resignation will close the book on a once promising political career than began when Ensign was elected to the House from the 1st district in 1994.

After two terms, he challenged Reid — losing by just 428 votes. Ensign quickly jumped into the open seat race caused by Sen. Richard Bryan’s (D) retirement in 1999. He won that race easily and quickly climbed the leadership ladder in the Senate, rising to the position of Republican Policy Committee chairman.

Ensign had begun to lay the groundwork for a possible presidential bid in 2012 when the news of his affair with Hampton broke. He insisted for months that he planned to run for re-election before bowing to the inevitable earlier this spring.

Aaron Blake contributed to this report.