The longer a politician stays in Washington, as a rule of thumb, the more difficult it becomes to keep his nose clean. Democrats ought to apply that reasoning and skip over Maxine Waters if they're looking for a new conscience of the House.

After three decades in Congress, the California Democrat has a more than checkered past. But that didn't keep her from predicting President Trump's political demise. "Get ready for impeachment," Waters cryptically tweeted out of the blue on Trump's 61st day in office and without further explanation.

If Waters hasn't completely discredited herself already — last week, she claimed, sans evidence, that the salacious details about Trump contained in the BuzzFeed dossier were true — then a quick review of her record should be enough to dissuade Democrats from following her lead.

During the height of the 2008 fiscal crisis, Waters helped arrange a meeting between the Treasury Department and top executives of a bank where her husband was a shareholder. Using her post on the House Financial Committee as leverage, she called Treasury Secretary Henry Paulson personally, asking him to meet with minority-owned banks.

When Treasury followed through, there was only one financial institution present: OneUnited. Had that bank gone under, the New York Times reported, Waters' husband would've lost as much as $350,000. Luckily for the Waters family, OneUnited received a cool $12 million in bailout funds.

After three years of special investigation, the ethics committee eventually ruled that Waters didn't technically break any rules. But that ruling came after unearthing her more than questionable family business practices, like making her grandson, Mikael Moore, her chief of staff.

Officially the committee ruled that Moore went behind the congresswoman's back to continue to lobby for special treatment. At best, that shows that Waters runs a haphazard office. At worst, it suggests she deliberately took steps to avoid prosecution.

Either way, Waters isn't in a position to tweet lectures about the conduct of any politician. Democrats would be wise to avoid her advice.

Philip Wegmann is a commentary writer for the Washington Examiner.