WASHINGTON — Nevada Sen. John Ensign, facing an ethics investigation stemming from an affair with a campaign aide, said Monday he would not seek re-election because he wanted to spare his family from an "exceptionally ugly" campaign.
"At this point in my life, I have to put my family first," Ensign said at a news conference in Las Vegas.
GOP Rep. Dean Heller, who won three Nevada elections as secretary of state, is considered the party's best candidate to retain the seat.
In February, the Senate Ethics Committee named a special counsel to investigate claims that Ensign violated ethics rules and federal law in the aftermath of his affair with Cynthia Hampton, a campaign aide married to Douglas Hampton, another Ensign aide and close friend.
Ensign acknowledged the affair in 2009, after Douglas Hampton threatened to go public. Ensign later acknowledged that his parents had paid Cynthia and Douglas Hampton $96,000 after Douglas Hampton left his job in the senator's office.
The Hamptons have suggested the payment was severance, but liberal critics have termed it an improper campaign contribution to Ensign by his parents. Ensign called the payment a gift.
Ensign is the eighth Senate incumbent to opt out of running for a new term, out of 33 seats that will be in play in 2012.
The Democratic Senate Campaign Committee said in a statement that the seat was "ripe for a Democratic pickup," citing trends in voter registration and the presence of President Obama at the top of the 2012 ticket.
Ensign will become the third Republican to announce his retirement. Four Democrats and one independent who caucuses with the party have announced they will not seek re-election.