I’ve just written this Jurisprudence commentary for Slate. It begins:

It’s nothing new to accuse your political opponents of allowing foreign money to be used in a U.S. election, as President Obama did this week with the U.S. Chamber of Commerce. In 2008, Republicans demanded an audit of the Obama campaign, because federal law did not require the campaign to disclose contributions of less than $200, and Republicans said some of that money could be coming from foreign individuals or governments. Before that, Senate Republicans investigated Bill Clinton over possible Chinese government money influencing the 1996 election.
We owe the recurring controversy to the inadequacy of our campaign-finance disclosure laws, which don’t allow for random audits of political committees to make sure the foreign money is kept out or segregated for nonpolitical purposes. And the Supreme Court reignited this issue in its divisive Citizens United opinion last term by specifically leaving open the question whether the ban on foreign spending in U.S. elections violates the First Amendment. As Democrats broadcast their breathless allegations that Republicans and the Chamber of Commerce are taking “secret foreign money to influence” the midterm elections, the real problem is why the logic of Citizens United can’t justify a ban.