President Donald Trump's sprawling corruption may never be brought under lawful control, especially with Senate Majority Leader Mitch McConnell acting as inside man in Trump's impeachment trial. But if Trump is ever to be punished for his many abuses of power, it just might be for his disregard of the nation's ineffectual and much-maligned body of campaign-finance law.

True, it's unlikely. Campaign-finance violations are often treated as clerical errors. The Federal Election Commission is a punchline in Washington, incapable of even voting on enforcement measures, since it lacks a quorum. (Both the White House and the Senate appear to like it that way.) Even when the commission did function, the most blatant disregard of campaign-finance law sometimes resulted in only weak fines administered many years late.

Yet the rule of law sometimes has a roundabout way of making the guilty pay. Al Capone went to prison for tax evasion. Richard Nixon was forced from the presidency over a botched burglary. And amid the thuggish efforts to insulate Trump from the democratic accountability of fair elections, campaign-finance laws are proving stubbornly relevant.

The laws include a "broad prohibition on foreign national activity" in U.S. elections. Foreigners are prohibited from contributing money or any "thing of value" to a campaign. They are also prohibited from spending money "in connection with any federal, state or local election in the United States." Thus Russian President Vladimir Putin's sabotage in 2016 was not just a crime against democracy _ it was an illegal in-kind contribution to the Trump campaign.

Special Counsel Robert Mueller acknowledged in his report that Donald Trump Jr.'s eager embrace of Russian government assistance to his father's campaign in 2016 ("if it's what you say I love it") "implicates" U.S. campaign finance law. But Mueller chose not to charge Trump Jr., explaining that it would be difficult to prove that he had "willfully" violated the law.

Lev Parnas and Igor Fruman were not cut a similar break. Instead, federal prosecutors charged the two Soviet-born Trump supporters with funneling foreign money into U.S. political committees, along with a $325,000 donation from the pair's largely imaginary energy company, which lacked income or assets, to the pro-Trump SuperPAC America First Action.

After laying low following their October arrest, Parnas has been quite a noisy fellow lately, appearing for interviews on television. Claiming that he fears that he's been set up as the fall guy, Parnas has further implicated the president and others in a scheme for which there was already ample evidence: Trump's effort to extort foreign assistance to his re-election campaign in the form of a Ukrainian investigation designed to smear former Vice President Joe Biden. The Ukraine scheme, Parnas told CNN, "was all about 2020."

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Parnas has been sharing photos of himself in intimate settings with the president, along with texts and other carefully curated details of his whirlwind romance with the MAGA crowd, including Rudolph Giuliani. Efforts to distance the White House from Parnas are complicated by an October letter to Congress from Trump's former lawyer John Dowd, which asserts that "Parnas and Fruman assisted Mr. Giuliani in connection with his representation of President Trump." There are lots of questions and surely more to the story, including the possibility that Giuliani and his friends were hoping to make a play for Ukrainian gas business. But there is no doubt about what inspired Parnas to sing: campaign-finance charges.

Attorney General William Barr, who buried the whistle-blower complaint about Trump's Ukraine scheme when it arrived at the Justice Department last summer, seems to recognize the potential of campaign-finance violations to trip up a president focused on committing heftier offenses. At a Senate hearing last May, he dodged rudimentary questions about foreign interference in presidential elections, calling it "a slippery area." He went to bizarre lengths to avoid labeling obviously illegal behavior out of bounds. Democratic Senator Chis Coons and Republican Senator Ben Sasse both appeared confounded by his testimony.

The federal agents in New York who charged Fruman and Parnas seem to have done some thinking about the implications of campaign finance law also. Announcing charges against the two men in October, FBI Assistant Director William F. Sweeney Jr. said:

The American people expect and deserve an election process that hasn't been corrupted by the influence of foreign interests, and the public has the right to know the true source of campaign contributions. These allegations aren't about some technicality, a civil violation or an error on a form. This investigation is about corrupt behavior and deliberate law-breaking. The FBI takes the obligation to tackle corruption seriously _ there are no exceptions to this rule.

At the same news conference, U.S. Attorney Geoffrey Berman said: "We will not hesitate to investigate and prosecute those who engage in criminal conduct that draws into question the integrity of our political process." Maybe it was prosecutorial boilerplate. But it sure sounded like a very pointed message to someone.

Francis Wilkinson writes editorials on politics and U.S. domestic policy for Bloomberg Opinion. He was executive editor of the Week. He was previously a writer for Rolling Stone, a communications consultant and a political media strategist.