Several news organizations are reporting that Nevada Sen. John Ensign (R) -- who has already announced he's not running for re-election next year -- will resign his seat as soon as tomorrow. NBC News, however, has yet to independently confirm the news.
GOP Gov. Brian Sandoval would appoint Ensign's replacement.
The Las Vegas Sun's Jon Ralston broke the story, and said the resignation is "likely tied to the ethics invesigation involving the senator."
*** UPDATE *** NBC's Kelly O'Donnell confirms the news. Per O'Donnell's report:
In a letter to Vice President Biden tomorrow, Sen. Ensign will state that his resignation from office is effective as of May 3, 2011.
"It is with tremendous sadness that I officially hand over the Senate seat that I have held for 11," said Ensign. "The turbulence of these last few years is greatly surpassed by the incredible privilege that I feel to have been entrusted to serve the people of Nevada. I can honestly say that being a United States senator has been the honor of my life.
"I know that my staff has been devoted to helping those in our state when they needed our assistance the most, and I hope that this will be the enduring legacy that we leave behind. As I close the door to this chapter of my life, I am left with memories that I will forever treasure. Traveling across our state during the years, I have heard incredible stories of strength, of struggle, and of compassion. I have met people who have forever changed me, and I can say that I will go through life a better person because of the struggle that I have been through and the support that I have received.
"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. For my family and me, this continued personal cost is simply too great.
"I am gratified that, after extended investigations, both the Department of Justice and the Federal Election Commission saw no grounds on which to charge me with improper conduct. I was hopeful that, with the closure of these investigations against me the wear and tear on my family and me would soon be over. This was not the case.
"As is its right, the Senate Ethics Committee is continuing its investigation of issues into which it has been inquiring for the past year and a half. Indeed, the Committee even decided recently to devote more resources to its investigation by hiring an outside counsel even though the issues have been viewed and reviewed by so many others.
"I came to office with the pledge to make this country a better place, but that pledge does not end with my resignation. I will continue to fight for a better country and for a future that our children deserve. I cannot fully express what serving the people of Nevada has meant to me, but I will try to repay them for their trust for the rest of my life.
"To the people of Nevada, I humbly say thank you for what you have given to me through the years. To my family, thank you for the support and love that you have shown me. To my staff, thank you for coming on this incredible journey with me and for standing by me despite the obstacles."