Sen. John Ensign won't seek re-election

Updated 3:23 p.m. Eastern Time

In what appears to be good news for the GOP, Nevada Republican Sen. John Ensign has decided not to seek a third term in 2012.

Ensign announced what he called "the most difficult decision that I have ever made in my life" in Las Vegas Monday. He said he decided not to run because of the toll a campaign would have taken on his family, telling reporters, "at this point in my life, I have to put my family first." 

A socially-conservative onetime rising star in his party, Ensign has been dogged by revelations that he had an affair with a former campaign aide named Cynthia Hampton, whose husband Doug had been Ensign's deputy chief of staff.

The Senate ethics committee is investigating Ensign in connection with his alleged efforts to help Doug Hampton find another job in the wake of the affair, as well as a $96,000 payment by Ensign's parents to the Hampton family.

The scandal has made Ensign a prime target for Democrats in what appears to be an uphill battle for the party to maintain control of the Senate in 2012. It has also made Ensign vulnerable to primary challenges; polls show that one potential challenger, GOP Rep. Dean Heller, holds a significant lead over Ensign in a head-to-head match-up. Another potential candidate is Tea Party Republican Sharron Angle, who lost a hard-fought campaign to Senate Majority Leader Harry Reid last year. 

Ensign has previously adamantly maintained that he would seek re-election, and he said Monday he came to his decision in the last few days. He said God and his wife had forgiven him for the affair and apologized "for the pain I have caused everyone." 

"There are consequences to sin, and when you are in a leadership role those consequences can effect a lot of people," said Ensign, who vowed to serve out the remainder of his term. He added that he did not want his family to have to see the television commercials that would have been run against him in a reelection campaign. 

The ethics investigation into Ensign has also roped in Oklahoma Sen. Tom Coburn, another conservative Republican who once lived with Ensign in a Capitol Hill home run by a Christian fellowship. Coburn has turned over more than 1,000 documents to Senate investigations as well as the Justice Department in connection with the investigation into Ensign.

The Justice Department announced in December that it would not seek criminal charges against Ensign.

Among the Democrats considering seeking the seat are Rep. Shelley Berkley of Las Vegas. Other names being discussed as potential candidates include Treasurer Kate Marshall, Attorney General Catherine Cortez Masto and Secretary of State Ross Miller.

There are currently 53 senators who caucus with the Democratic Party, giving the party a three-seat majority. While Democrats have 23 Senate seats to defend in 2012, Republicans must only defend 10, and GOP officials are optimistic about their party's prospects for taking control of the chamber.

Heller is widely seen as a stronger general election candidate than the embattled Ensign, which means that Ensign's decision not to seek another six-year term is welcome news for national Republicans.

Nevada and Massachusetts - where Republican Sen. Scott Brown is up for reelection next year - are the two states where Democrats see the best opportunity to mitigate the expected damage and potentially hold onto their majority.

"Nevada is now an open seat, and ripe for a Democratic pickup. It remains high on our target list," Guy Cecil, Executive Director of the Democratic Senatorial Campaign Committee, said in a statement Monday afternoon. "Whoever Republicans field as their candidate will have a tough time holding onto this seat in a blue-trending state with President Obama at the top of the ticket. Democrats will have the resources needed to win this seat and just as important, will build a grassroots organization that matches 2008 and 2010."

U.S. Senator John Cornyn, Chairman of the National Republican Senatorial Committee, said in a statement that the Nevada Senate race will "now come down to a clear choice between two competing visions for our country - between a Republican candidate who believes in smaller government, fiscal responsibility and creating good, private sector jobs, and a Democrat candidate who believes in keeping our country on the same reckless fiscal path of more government and higher taxes."

Four Democrats have now announced they are retiring in 2012 as well as an independent who caucuses with Democrats, Connecticut Sen. Joe Lieberman. Ensign is the third Republican to announce his retirement, joining Texas Sen. Kay Bailey Hutchison and Alaska Sen. John Kyl.