Sen. John Ensign, R-Nev., has landed in our No. 2 spot on Scandal Watch.

This post has been updated (June 19, 2009 6:40 p.m.)

The fallout from an extramarital affair between Ensign and Cindy Hampton, a campaign staffer, is threatening to ensnare other Republican leaders as they try to marshal opposition to the Obama administration.

A June 11 letter written by Hampton's husband, published today in the Las Vegas Sun, claims that at least one of Ensign's colleagues, Sen. Tom Coburn, R-Okla., knew about the affair more than a year before Ensign's public confession, but did not act to remove him from party leadership.

Though unconfirmed -- Coburn's communications director said Coburn would not comment on the claims made in the letter -- the allegation could turn one of Washington's periodic sex scandals into something of larger significance.

Initially, it seemed as though the splatter would be confined to Ensign's political ambitions. After admitting to the affair on Tuesday, Ensign -- a rising star among conservatives who was thought to be considering a presidential run in 2012 -- resigned his post as the Senate's fourth-leading Republican.

Then it emerged that Cindy Hampton's salary -- paid from Ensign's political payroll -- had doubled during the time of their affair, which went on from December 2007 to August 2008. Also in that period, Hampton's son landed a $1,000-a-month internship with the National Republican Senatorial Committee -- chaired by Ensign. After Hampton and her husband, Doug (also a top Ensign aide), were dismissed by Ensign, the senator allegedly helped Doug Hampton find a job with a Las Vegas airline that is among his major campaign contributors.

Now the Sun is reporting that, days before Ensign acknowledged his affair with Cindy Hampton, Doug Hampton wrote a letter to Fox News anchorwoman Megyn Kelly, begging her to help expose Ensign's "unethical behavior" because his fellow lawmakers had not.

The letter claimed that Doug Hampton had confronted Ensign repeatedly about the affair, including once in Ensign's Washington, D.C., home in February 2008 in front of "a group of his peers."

"One of the attendee's [sic] was Senator Tom Coburn from Oklahoma as well as several other men who are close to the Senator," it says.

Hours after the Sun posted the letter, Ensign fired back. His spokesman released a statement saying Doug Hampton had approached Ensign for a pay-off within the last month, making "exorbitant demands for cash and other financial benefits" through an attorney.

If indeed Coburn and others were aware of Ensign's problems for as long as Hampton says, they could face thorny questions about why his stature within the Republican Party continued to rise. Ensign was chairman of the Republican Senate Policy Committee, which sets out the party's legislative agenda, and just weeks ago, he traveled to Iowa, fueling the presidential speculation.

The controversy is a distraction Coburn hardly needs as he attempts to spearhead Republican opposition to the Obama administration's stimulus plan. Coburn recently issued a report criticizing 100 stimulus projects, then found himself in a dust storm when administration officials called the report misleading and error-filled.

Update (June 19, 2009 6:40): Hours after the Sun posted the letter, Ensign fired back. His spokesman released a statement saying Doug Hampton had approached Ensign for a pay-off within the last month, making "exorbitant demands for cash and other financial benefits" through an attorney.