Zephyr Teachout is an associate professor of law at Fordham University.
D.C. and Maryland plan to sue President Trump for violating a little-known constitutional provision called "the Emoluments Clause." (Jenny Starrs/The Washington Post)

In the middle of the 17th century, King Charles II of England took a secret pension from the French King Louis XIV. He agreed to a closer relationship, including a treaty that wasn’t clearly in England’s best interest. The precise content of the secret agreement wasn’t revealed for more than 100 years.

Today, 350 years later, the president of the United States is receiving payments from foreign countries. The money comes to President Trump by way of his companies, although the details and scope of his profits are secret; he refused to disclose his tax returns. After the election, Trump had several months to move toward liquidation and putting his assets in a truly blind trust. He has chosen, instead, to keep his ownership interests in his businesses, turning over operating decisions to his children but remaining an owner. His decision threatens the integrity of American democracy and national security, and it should ring alarm bells for all citizens, regardless of political party.

Trump’s choice violates one of the most overlooked but important sections of the U.S. Constitution, the foreign emoluments clause, which was framed to avoid problems of split loyalty such as that posed by Charles II. As a law professor, I began exploring the clause in 2009 while examining the framers’ near-obsession with protecting against corruption. The clause represented a deliberate break from European traditions, where financial relationships between a country’s representatives and other governments were common. And it epitomized “the particularly demanding notion of corruption” held by our framers.

I never expected the clause to be litigated: Presidents and federal officials have gone out of their way to avoid violating it. Until now. But Trump’s blatant violation of the clause is a violation of our fundamental document and our fundamental principles.

That’s why the nonpartisan watchdog group Citizens for Responsibility and Ethics in Washington filed suit in federal court this week to seek a declaratory judgment and injunction. I am one of the lawyers on the case.

The framers were trained to be wary of how human nature can be tempted, and of international incentives to tempt. As George Washington said later, “Few men have virtue to withstand the highest bidder.” Our Constitution was written in the hot summer of 1787 in Philadelphia, but the convention was haunted by recent European failures and the long-ago corruption of Rome. Secret money from foreign countries was a repeat topic, with the framers wary of the “melancholy picture” of foreign intrusions and intrigues. The British experience with Charles II was a warning that even heads of state could be influenced by foreign powers.

The framers understood that humans are inclined to look more favorably upon those who are responsible for their wealth. In private affairs, warmth toward someone who has given a gift, or with whom one has a good business relationship, is a positive emotion that enables human connection. But in public affairs, that sometimes-unconscious influence can be insidious. The framers had also seen how George III used his power to create a side employment relationship with parliamentarians he wanted to influence.

So the Constitution includes more than a dozen anti-corruption provisions, several of which are targeted specifically to protecting against foreign influence. For instance, only natural-born citizens can be president, foreigners are not allowed to hold federal office and a long residential period is required so candidates would not be mere tools of wealthy foreign powers.

The foreign emoluments clause prohibits federal officers from accepting foreign “gifts,” “emoluments” and “titles of nobility” without congressional consent. As a recent white paper by Harvard Law professor Larry Tribe and attorney Joshua Matz explains, extensively citing the meaning of the word at the time of the Constitutional Convention, emoluments include the profits an official receives in the course of business relationships.

The emoluments clause did not come easy: The rule was such a serious break from European tradition that its adoption caused problems for several decades, as other countries were likely to take offense when they attempted to give gifts in violation of the clause. President Martin Van Buren had to write a letter to the Imam of Muscat, telling him he could not accept horses, pearls, a Persian rug, shawls and a sword because it was a “fundamental law of the Republic which forbids its servants from accepting presents from foreign States or Princes.” The framers knew what a headache it could become, but they included it anyway because of the lessons of history. They knew that foreign governments would necessarily attempt to influence U.S. policy, and they wanted the Constitution to protect against that.

Some corruption rules rely on proof that a deal happened, an explicit arrangement exchanging something of value for a political action, with intent to trade. Such laws are notoriously difficult to prosecute, because it is rare that either of the parties to an explicit bribe would come forward to report a crime. The laws apply well to the Keystone Cops of politics, clumsy lawmakers who take sacks of cash in the IHOP bathroom.

The emoluments clause, however, does not require direct proof of anything untoward, and that is essential to its effectiveness. The most powerful anti-corruption rules are prophylactic, forbidding a whole category of relationships that are likely to lead to corruption.

Consider the countries we know are making payments to Trump companies through state-owned entities, payments that affect Trump’s wealth: China and the United Arab Emirates, both at the heart of regions critical to U.S. foreign policy. Then consider the longer list of countries in a position to benefit him because of business relationships Trump has, including India, Indonesia, Turkey, the Philippines, Great Britain and Vietnam. This is just a beginning sketch of what we know so far; Russia, Saudi Arabia and Taiwan reportedly may also be involved with Trump businesses. The benefits come from a range of relationships: The Qatari state airline pays rent at the Trump Tower in New York; entities in Britain, Bulgaria, Brazil, Indonesia and Vietnam reportedly make licensing payments for the rights to produce local versions of “The Apprentice,” Trump’s reality TV show; his developments in India require governmental permitting, which under the law would be a forbidden benefit.

Each of these countries, and possibly more, now has a direct mechanism to attempt to influence the president. What’s more, every time Trump makes a foreign policy decision that relates to any of these countries, citizens will wonder whether he, like Charles II, put his own financial interest ahead of American jobs, or whether he is engaging in or refraining from military action because of a business relationship.

Trump’s lawyers made a strange concession in a news conference recently, announcing that Trump would donate all profits from foreign government payments to Trump hotels to the U.S. Treasury. The suggestion was that the donation mooted the problem. But another unspoken implication was that there is something troubling about foreign-derived profits. The donation does nothing to address the Constitutional violation, which occurs at the moment of accepting the benefit, even if Trump’s hotel loses money on the transaction. It merely means that some of his constitutional violations will be followed by a payment of penance. Moreover, profits from the hotels represent only a part of the foreign benefits that are flowing to him — none of his office towers, condo or apartment sales, licensing agreements or loans on other properties are covered at all.

The donations appear to be a nod to how presidents have treated foreign gifts: with statutory permission of Congress, they have donated them to the Treasury or National Archives. (That proved tricky when Bulgaria gave George W. Bush a puppy.) In those instances, the donation was appropriate because it flowed from consent by Congress, which the Constitution requires. The point of strong corruption laws like the emoluments clause is that they take the president out of the position of being the judge of inappropriateness. In Trump’s case, though, he has proposed that an official at his company will do exactly that.

Even Trump will, on occasion, acknowledge the seeds of a problem. Of Turkey, he said, “I have a little conflict of interest ’cause I have a major, major building in Istanbul.” At a news conference this month, he announced that he would not engage in deals in Russia because it would present a conflict. (The Washington Post reported last year on “strong evidence that Trump’s businesses have received significant funding from Russian investors.”) If there’s a conflict with Russia, there is a conflict with every country. More important, since Trump hasn’t disclosed any information about his finances, how would we know?

These are not trivial potential conflicts. They strike at the heart of what it means to be president: undivided loyalty to one’s country. The least Trump can do is stop violating the Constitution by accepting secret money from foreign governments.