Sen. John Ensign’s resignation aims to halt a nearly two-year Senate ethics investigation and spare the two-term Nevada senator and his family a public trial.



Political handicappers say it could also give Republicans an edge to hold on to a seat expected to be highly competitive in 2012. Senator Ensign’s replacement will be named by a Republican governor and stands to pick up the typical incumbency advantage.



But in fact, neither of those outcomes is clear. In a joint statement, leaders of the Senate ethics panel said that “the Senate Ethics Committee has worked diligently for 22 months on this matter and will complete its work in a timely fashion.”

Shaking up 2012: US senators who aren't running for reelection

“Senator Ensign has made the appropriate decision,” said the panel’s chair Barbara Boxer (D) of California and vice-chair Johnny Isakson (R) of Georgia, in a statement. That could include the public release of findings and documents that Ensign had hoped to avoid.



The details of Ensign’s admitted affair with a former aide – and the cash and political favors around it – made Ensign’s Senate seat a top prospect for Democrats in 2012.



Until last month, Ensign had committed to defend his seat, claiming that he had broken no law.

But his decision to not seek reelection, announced March 7, opened up a highly competitive GOP field. Nevada Gov. Brian Sandoval (R) of Nevada is expected to appoint three-term Rep. Dean Heller (R) of Nevada, who is already in the Senate race, to replace Ensign.

Rep. Heller a strong conservative

Congressman Heller, a former stockbroker, state assemblyman, and Nevada Secretary of State, would add a strong conservative voice to the Senate Republican caucus.

In recent House votes, Heller broke with GOP leaders to oppose a spending bill for FY 2011 on the grounds that it did not cut deeply enough. He also backed a failed conservative bid to cut non-defense discretionary spending to FY 2006 levels.

“The truth no one is likely to admit is that Sen. Ensign is being pushed out to give the Republican party a leg up in the 2012 election by allowing Governor Brian Sandoval to appoint Rep. Dean Heller (R) of Nevada to the seat so he can run with all the advantages of incumbency,” said Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, in a statement Friday.



Typically, incumbency is worth at least a 5-point advantage on election day, but appointees historically haven’t reaped the same advantage. Since 1913, of the 189 people who have been appointed to vacant Senate seats, only a third were later elected to those seats. Of those who opted to run for election (70 did not), 62 won their races and 57 were defeated, according to the Senate Historical Office.



Here’s what’s not in dispute: Should Congressman Heller be appointed to Ensign’s Senate seat, his House seat becomes a key bellwether for the 2012 campaign cycle.



But Nevada has never had a special election for a US House seat, and state law is unclear on how to proceed.

Special House election could be a free-for-all

One possible interpretation is that the election is a free-for-all, with any candidate able to file to run – and possibly win with as little as 20 percent of the vote. Under such a scenario, former GOP Senate nominee Sharron Angle, a tea party favorite, could be a credible candidate.

But if the nomination comes down to a decision by state party leaders, Angle, viewed as running a poor race against Senate majority leader Harry Reid in 2010, is highly unlikely to be the GOP nominee. If she ran as a third-party candidate, it could split the Republican vote, giving the seat to a Democrat.



“Nevada is the center of the political world for now,” says David Wasserman, who covers House races for the Cook Political Report. “You have an open Senate race that’s likely to be very competitive, you could have as many as four competitive House races, depending on redistricting, and you have a presidential battleground. What more can you ask for.”

In a statement Friday, Gov. Sandoval said, “I expect to announce an appointment before [Ensign’s] resignation effective date of May 3. I take very seriously the importance of this appointment, so to speculate on potential candidates for appointment before then would be premature.”

Shaking up 2012: US senators who aren't running for reelection