The problem is that legally, his argument doesn’t get him where he wants to go. Even though Mr. Trump can give his campaign as much of his own money as he wants to, he can’t ask other people to front the money for him and promise to pay them back later without reporting the arrangement in a timely fashion to the Federal Election Commission. But he didn’t report it, subverting the whole point of the nation’s post-Watergate campaign finance laws, which is to disclose campaign giving and spending to the American people before an election — not 20 months later.

But, the Trump defenders say, reporting violations happen all the time, and that is certainly true. But there are two facets that make the Trump reporting violations criminally significant, as opposed to a misdemeanor oversight or bureaucratic snafu: It appears to have been an intentional end-run around the campaign finance laws and to involve a conspiracy. Each of these points explains why the new Trump argument will fail.

Criminal law focuses on mens rea, or criminal intent. This means the very same act can be criminal if done with one state of mind and innocent if done with another. It is a mistake to think about Mr. Cohen’s allegations as some sort of routine paperwork error. Structuring a transaction to intentionally avoid reporting it as required by the law is a very serious offense, not a technical one that can be forgiven. That is particularly true of the secret payments to the two women, which, had they been disclosed before the election, as they should have been, might have altered the outcome.

The second facet is even more problematic for the president. Prosecutors use the conspiracy doctrine to punish two or more people who merely agree to commit a criminal act. They don’t even have to actually perform the act; they just need to have agreed to do so. The idea behind conspiracy liability is that when two people agree to commit a crime, it’s much worse for society than when a lone actor does. A Yale Law Journal article I wrote on this subject was inspired by a riddle: Why is it that if you sell a joint, you get a six-month sentence, and if your friend sells a joint, he gets a six-month sentence, but if you both agree to sell a single joint, you get a five-year minimum sentence? The outcomes seem really odd because it looks as if the same crime is getting different punishments.