The nerd caucus of the United States Senate is currently headed by Richard Blumenthal, the Connecticut Democrat, who clerked for Justice Harry Blackmun on the Supreme Court before serving for two decades as his state’s attorney general. (Other members of the group include Mike Lee, of Utah, who clerked for Samuel Alito before he was appointed to the Supreme Court, and Ted Cruz, a law clerk for William Rehnquist, who aspires to greater political heights than caucus membership usually allows.) Still, for all of Blumenthal’s legal experience and expertise, he admits that when Donald Trump was elected, last year, he had never heard of the emoluments clause of the Constitution.

Blumenthal has since discovered that the clause addressed a major issue for the Framers, who feared that wealthier countries would bribe the new nation’s public-office holders. “We were a nation flat on our back, and we had created a system without permanent office holders—no kings, no lords—so it would be clear that people would be moving in and out of government,” Blumenthal told me the other day. “And rich countries were all too willing to take advantage economically of the people who were in government at any given time.” The addition of the clause to the Constitution was apparently prompted by Louis XVI’s gift of a miniature portrait of himself, set in a diamond-encrusted case, to Benjamin Franklin, when Franklin completed his service as Ambassador to France.

Accordingly, Article I, Section 9 states: “No Person holding any Office of Profit or Trust under them [the United States], shall, without the Consent of the Congress, accept of any present, Emolument, Office, or Title, of any kind whatever, from any King, Prince, or foreign State.” For more than two centuries, the clause remained an obscurity, rarely addressed by the courts, but then Donald Trump became President and, more to the point, declined to cut ties with his far-flung business interests. Foreign countries, which want to ingratiate themselves with the new President, have flocked to Trump’s businesses, especially to the Trump International Hotel, in Washington, D.C., creating a modern version of the problem that the Framers tried to address. So Blumenthal joined forces with the Constitutional Accountability Center and became the lead plaintiff in a lawsuit filed against the President, last week, for violating the emoluments clause. Thirty other Senators and more than a hundred members of the House of Representatives, all Democrats, have joined as co-plaintiffs.

Other lawsuits against Trump, on emoluments grounds, have been filed, including one by the governments of Maryland and the District of Columbia (none have yet been decided), but Blumenthal believes that his suit will be the one that survives a challenge on standing grounds. “The clause specifically says that the President needs the consent of Congress to receive this money from foreign countries, so he’s deprived us of the chance to give our consent,” Blumenthal said. “I think that’s enough for us to get into court.” Notably, if Judge Emmet Sullivan, of the federal district court in Washington, allows the case to proceed, the plaintiffs may be allowed to obtain Trump’s elusive tax returns as part of the discovery process.

In one of the other cases filed against Trump earlier this year, brought by Citizens for Responsibility and Ethics, the Justice Department argued that the case should be thrown out because “the Emolument Clauses apply only to the receipt of compensation for personal services and to the receipt of honors and gifts based on official position. They do not prohibit any company in which the President has any financial interest from doing business with any foreign, federal, or state instrumentality.” To respond to that argument, Blumenthal and his lawyers found an unlikely potential ally—the young Samuel Alito, who wrote a legal opinion about the clause in 1986, during the Reagan Administration, when he was a lawyer in the Justice Department’s Office of Legal Counsel. The issue in that case was less than momentous: whether a NASA scientist could accept payment of a hundred and fifty dollars for reviewing a Ph.D. thesis at the University of New South Wales, in Australia. Alito concluded that the scientist could keep the fee, because the university was not a “foreign state,” but he took an otherwise hard line on the clause, writing that it “is directed against every kind of influence by foreign governments upon officers of the United States.”

Blumenthal’s complaint in this case identifies several ways that foreign governments may have sought to influence Trump, in addition to booking rooms at the Trump International and at other Trump hotels around the world. The Chinese government has awarded trademarks to Trump businesses; entities affiliated with the governments of China and the United Arab Emirates have rented space in Trump buildings in New York City; the BBC, which is funded, in part, by the government of the United Kingdom, has licensed “The Apprentice,” Trump’s television series.

As a remedy, Blumenthal is seeking an order forbidding Trump’s businesses from receiving any further payments from foreign governments. This, of course, might require Trump to sell the businesses rather than bar the customers. “Trump has said that these businesses are too large and complex to sell, but that’s not our problem. Nobody said he had to run for President,” Blumenthal said. “Why should he be above the law?”