This piece was originally published on Just Security, an online forum for analysis of U.S. national security law and policy.

The special counsel’s indictment on Friday of Russian individuals and organizations brought campaign finance law for the first time into formal charges in the case of Russia’s interference in the 2016 election. But this development came with a mystery. The indictment alleges facts that support charges of federal campaign finance law violations—such as the prohibition on foreign national contributions—but does not charge any such offenses. This is clearly not for want of evidence, since the indictment sets out in considerable detail the millions in foreign national spending to influence the 2016 election. Yet Bob Mueller omitted any direct charge for violations of the Federal Election Campaign Act.

Instead, the indictment builds the campaign finance issues into a conspiracy to defraud the United States—it alleges that the Russians conspired to obstruct the capacity of the Federal Election Commission to enforce the law. The act of obstruction was a failure to report their illegal expenditures. If the FEC did not know about the expenditures, it could not enforce the law.

Now, of course, those engaged in illegal campaign finance activity, such as spending from foreign national sources, won’t ever make an exception and comply with self-incriminating reporting requirements. And the irony of the premise—that the FEC would get the job done if given the needed facts—will not be lost on those who have observed the agency’s decline. But there is a theory, of course, behind the structure of the charges, and it might hold a clue to what comes next in the campaign finance portion of the case.

Mueller and his team may have concluded that straight statutory campaign finance allegations rest on too much untested ground and would complicate what may well be the next phase of their investigation. This consideration would not affect the foreign national side of the case: Foreign nationals are plainly prohibited from spending in the manner detailed in the indictment. But how the law reaches American co-conspirators is less certain, and the special counsel’s theory of the case, pleading the campaign finance aspect of the case through conspiracy-to-defraud, may allow more securely for the prosecution of American actors.

In other words, if Mueller’s case for campaign finance violations affected only Russians, there would be no obvious reason to exclude Federal Election Campaign Act violations from the indictment. Russians spent substantial sums to influence an election, as expressly laid out in the charging document, and this is an unambiguous violation of federal law. If, however, Mueller possesses evidence of Americans’ complicity in these violations, he may have decided on a different theory of the campaign finance case that more reliably sweeps in U.S. citizen misconduct.

On the face of it, the law prohibits a U.S. campaign or person from “soliciting” something “of value” from a foreign national, and it bars rendering “substantial assistance” to illegal foreign national spending. It seems clear that the facts known to date implicate these rules. It is also true that there is little precedent and arguably an increased risk of a defense grounded in the “vagueness” of these prohibitions.

Some commentators have expressed unease about the constitutional limiting principle that would govern the enforcement of these provisions. I do not share this view, but it is held strongly in some quarters and, therefore, appropriately and respectfully noted.

The Mueller indictment is conceivably one way to solve this problem. It alleges a conspiracy to prevent the FEC from taking up and addressing the regulatory issues, and American co-conspirators may be brought in on any overt act in furtherance of this illegal scheme. Any U.S. citizen who intentionally supported the Russian electoral intervention could be liable. Examples would include U.S. citizens engaged in conversations like those in Trump Tower in the summer of 2016, or Donald Trump Jr.’s communications with WikiLeaks. The conspiracy to defraud the United States could also envelop any Americans who helped cover the Russians’ illegal electoral program by lying to federal authorities about the campaign’s Russian contacts.

The special counsel may well have concluded that he could deal with any instances of U.S. citizen complicity without getting bogged down in unresolved questions of what constitutes “soliciting” support or providing the foreign national with “substantial assistance.” In sum, Mueller and his team may have adopted this theory of the case to facilitate the charging of Americans who helped their Russian allies interfere in the 2016 election. This is perhaps the most plausible solution to the Mueller indictment mystery.

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