When you stretch the law to “get” a political opponent, it’s rarely possible to return the law to its original shape. Which brings us to Stormy Daniels.

Shortly before the 2016 election, one of President Trump’s lawyers, Michael Cohen, arranged a $130,000 payment to the porn star in return for silence about a 2006 affair she claimed to have had with Mr. Trump. (Both the president and Mr. Cohen have denied the affair; Mr. Trump has said he did not know of the payment to Ms. Daniels until this February.)

Not satisfied with an old-fashioned sex scandal—perhaps because the president seems impervious to that—some want to turn this into a violation of campaign-finance law. Trevor Potter, a former member of the Federal Election Commission told “60 Minutes” the payment was “a $130,000 in-kind contribution by Cohen to the Trump campaign, which is about $126,500 above what he’s allowed to give.” The FBI raided Mr. Cohen’s office, home and hotel room Monday. They reportedly seized records related to the payment and are investigating possible violations of campaign-finance laws.

But let’s remember a basic principle of such laws: Not everything that might benefit a candidate is a campaign expense.

Campaign-finance law aims to prevent corruption. For this reason, the FEC has a longstanding ban on “personal use” of campaign funds. Such use would give campaign contributions a material value beyond helping to elect the candidate—the essence of a bribe.