Congressional Democrats will seek President Donald Trump’s tax returns if a judge agrees to hear a suit accusing him of violating the foreign emoluments clause of the U.S. Constitution, Sen. Richard Blumenthal said Thursday following oral arguments in D.C. federal court over an effort to quash the case.

President Trump’s tax returns, which have been a source of controversy since early in the 2016 presidential campaign, would be among the documents federal lawmakers would seek in order to identify potential undeclared payments or benefits bestowed on the president by foreign governments, the Connecticut senator said following a hearing on Trump’s motion to dismiss the suit for lack of standing.

“Discovery in this case would appropriately include tax returns,” Blumenthal said.

The suit, filed last June by 30 members of the U.S. Senate and 166 members of the U.S. House of Representatives, led by Blumenthal and Rep. Jerrold Nadler, D-N.Y., accuses the president of violating the emoluments clause by continuing to profit from his sprawling private business, the Trump Organization, while in office, including through payments, loans and regulatory actions from foreign governments, without the consent of Congress.

No Republicans have signed on to the suit.

During oral arguments held just blocks from President Trump’s eponymously named D.C. luxury hotel, a symbol for critics of the overlap between Trump’s public duties and private interests, the Constitutional Accountability Center’s Brianne Gorod urged U.S. District Judge Emmet G. Sullivan to grant Democratic lawmakers standing in the case, saying members of Congress have been directly harmed by the president’s acceptance of payments from foreign governments without notifying or seeking consent from them as required by the Constitution.

The president, Gorod said, is prohibited from accepting any gifts or payments from foreign governments without first obtaining affirmative consent from Congress by the Constitution’s requirement that “[N]o Person holding any Office of Profit or Trust under [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.”

By failing to disclose the extent of his business dealings with foreign powers, Gorod said, President Trump has deprived members of Congress of their right to even hold a vote on whether to permit the acceptance of such “emoluments.”

“Congress can’t take that vote as long as the president is taking these emoluments in secret without the knowledge of Congress,” Gorod said.

The U.S. Department of Justice’s Brett Shumate shot back, saying the emoluments claims amount to a political dispute between members of Congress that courts have historically said should be resolved through political mechanisms.

Congress, Shumate said, could pass a law if it wishes to prevent the president from accepting emoluments.

“There are always going to be disputes between the president and Congress,” Shumate said. “These disputes should be resolved through the political process.”

But Gorod said the instant case is unlike other disputes between the president and Congress, because traditional tools used to check presidential power aren’t relevant.

Because Trump’s business entanglements don’t rely on the use of federal funds or personnel, Gorod said, Congress can’t rely on the power of the purse to try and pressure him into compliance with the emoluments clause.

Further, Congress’ ability to vote on new legislation related to emoluments doesn’t resolve the fact that its members have been deprived of their constitutional authority to weigh in on the payments before they reach the president.

According to Gorod, the emoluments clause requires “affirmative consent” by Congress for any payment or benefit to the president. So by failing to hold a vote, Congress has effectively denied consent for any foreign government payments to the Trump Organization. 

Requiring Congress to pass new legislation prohibiting foreign payments to the president, Gorod added, would “effectively wipe the emoluments clause out of existence.”

That’s because such a ruling would create the presumption that the president can accept as many foreign gifts as he wants absent Congressional action, Gorod said, adding that such a presumption would effectively reverse the restrictive language in the Constitution.

Questions about transparency issues and potential conflicts of interest with Trump’s privately owned business first arose during the 2016 presidential campaign when then-candidate Trump refused to publicly release his tax returns, breaking with decades of tradition by presidential contenders and his own campaign trail promises.

Those questions intensified when Trump refused to fully divest from his business when he took office in January 2017.

The instant suit is one of at least three civil suits targeting the flow of foreign money toward the Trump Organization, but in a Wednesday conference call Blumenthal noted the instant case represents the broadest challenge to the president’s ability to continue to receive foreign payments through his businesses.

An axed civil suit in New York and an ongoing case in Maryland federal court both focus only on alleged damages suffered by local businesses that must now compete with Trump’s properties for business.

The federal judge overseeing the Maryland case has said the plaintiffs can only raise issues of competitive harm caused by activities at Trump’s D.C. hotel, which has hosted multiple events for foreign governments, and which attorneys general for Maryland and D.C. claim enjoys an unfair advantage over competitors due to its ties to the president.

The suit from federal lawmakers, by contrast, is the only suit seeking Congressional oversight of all payments and benefits provided to the Trump Organization by foreign governments, Blumenthal said.

Rep. Nadler, speaking after the hearing, said Congress must be permitted to enforce the emoluments clause in order to ensure that the president is acting in the country’s interest rather than his own.

“The emoluments clause is the main anti-corruption provision to the Constitution, and Congress must enforce it,” Nadler said.

The plaintiffs are represented by Brianne J. Gorod, Elizabeth B. Wydra and Brian R. Frazelle of the Constitution Accountability Center.

Trump is represented by Brett A. Shumate and Jean Lin of the U.S. Department of Justice.

The case is Blumenthal et al. v. Trump, case number 1:17-cv-01154-EGS, in the U.S. District Court for the District of Columbia.