The House ethics committee announced late Monday afternoon that it would launch a formal investigation into Rep. Shelley Berkley (D-Nev.). At issue is whether her legislative actions were meant to help her husband’s business.

And it comes at about the worst possible time for her — less than four months before she is on the ballot for an open Senate seat.

Rep. Shelley Berkley (D-Nev.) hosts a "Congress on Your Corner" event in January 2011. (Marlene Karas for The Washington Post)

Nevada is a battleground state, among the swingiest swing states in the country. And given that this is basically an open-seat race (Republican Sen. John Ensign resigned amidst his own ethics issues last year), this race was destined to be among the most contested in the country. Polling throughout the race has shown that to be the case, with Heller demonstrating a very small lead in the latest surveys.

A New York Times report in September accused Berkley of using her congressional office to help her husband’s nephrology practice and dialysis business. Most notably, she helped save a kidney transplant center in the state and wrote a letter to a House colleague warning against changes to doctors’ compensation for dialysis treatments.

That’s the backdrop.

What the ethics committee’s decision means is that Republicans, from now until Election Day, can barrage Berkley with ads noting that she is “under investigation” for congressional actions that appeared to benefit her husband’s business. And barrage they will. Expect to see “under investigation” in just about every GOP-funded ad in this race.

In addition, this kind of thing tends to define a candidacy. Even though Berkley has not been found guilty of any wrongdoing, the fact is that the ethics committee found enough suspicious about her actions to warrant the formation of an official panel to look into it.

Suddenly, this is not just a New York Times report that made some waves a year ago. Instead, it is a credible and official set of allegations that Berkley is going to have to confront throughout the remainder of her campaign. This means that local media won’t have any qualms about referring to the controversy.

(In addition, this isn’t the first time that Berkley has been accused of mixing politics with personal gain; in 1996, before joining Congress, she urged then-boss Sheldon Adelson to contribute money to judges and offer favors to county commissioners to curry favorable rulings and decisions. She later apologized. Expect to hear about this as well.)

Make no mistake: She has an ethics cloud over her. And it will stay there.

“This could be fatally toxic to her candidacy,” said Nevada politics expert Jon Ralston. “It’s especially troublesome in the key county of Washoe, where these headlines will have more resonance because she is less known. However, it is mid-July and the quality of the campaigns will matter, so she still has a chance. But this has to be very depressing for Democrats.”

One thing Berkley and Democrats don’t have to worry much about, though, is any further news from the ethics investigation. Given the traditionally slow-moving ethics process and the fact that lawmakers will probably have a light schedule in Washington in the runup to the November election (to focus on their own reelection races), it seems unlikely that there will be a final verdict before then. And the committee doesn’t say anything about a case while it’s under investigation.

In other words, barring some more enterprising reporting on this subject by the media, being “under investigation” is about as bad as it’s going to be for Berkley.

Democrats also note that the difference between being “under investigation” — present tense — and having been under investigation in the past is most likely negligible in the minds of voters. In other words, Republicans could — and have — run ads noting that she is/was under investigation, and whether that’s present or past tense, they were going to run that ad.

They also note that the main thing she is accused of doing to benefit her husband — saving a kidney transplant center — also benefitted the state. And as a Berkley ad from June notes, Heller himself was on board with that effort.

Thirdly, they note that the state has, in the past, been able to stomach some ethical uncertainty (after all, what happens in Vegas ... ). Former governor Jim Gibbons (R) eventually succumbed to his ethical and personal problems and lost his primary in 2010. But he was easily elected in 2006, even with some of those issues hanging over his head, including an alleged assault on a cocktail waitress and a Wall Street Journal report on the eve of the election that suggested that he accepted personal favors in exchange for his actions as a then-congressman.

All fair points.

But as the race comes into focus, the risk for Berkley is that the ethics cloud hanging over her head begins to define her candidacy. If voters have legitimate concerns that she is feeding at the public trough, it could sway them in a state where voters are very swayable.

And above all: Being under investigation is not helpful, and in a race that will likely be decided by a few points, it could make the difference between Sen. Heller and Sen. Berkley.