In a novel lawsuit filed by Sen. Richard Blumenthal, D-Conn., against President Donald Trump alleging violations of the Constitution’s emoluments clause, appeals judges on Monday questioned the senator’s standing to sue, while grappling with tough questions about how else Congress could conduct oversight of the president.

It’s unclear how the judges will rule in this latest legal square-off between Democrats and the president.

“I was encouraged,” said Blumenthal. “At the end of the day, they clearly focused on the fact that Congress cannot provide a remedy for this blatant and flagrant violation of the emoluments clause unless we are given the relief we are seeking.”

As House Democrats conducted another impeachment inquiry hearing Monday, the protracted lawsuit represents another line of attack for legislators who suspect the president has acted improperly. A ruling is expected sometime in the next few months.

The case highlights several unprecedented aspects of the Trump presidency. Unlike other presidents, Trump is an international businessman, who has retained ownership of his hotels and other properties during his term. The real estate mogul has also distinguished himself by strongly resisting numerous attempts of congressional oversight into his finances, his campaign and his foreign policy — most notably toward Ukraine, the subject of the impeachment inquiry.

Blumenthal’s lawsuit is one of three major cases testing for the first time the Constitution’s ban on American elected officials engaging in private business relationships with foreign governments.

The case hinges on whether the president needs congressional approval before doing business with a foreign government. Blumenthal, the lead plaintiff among 200 Democratic lawmakers who sued Trump, believe Trump needs that congressional approval and never got it, placing him in violation of the Constitution. Connecticut’s entire Congressional delegation has backed Blumenthal in the lawsuit.

Counsel for Blumenthal argued before the U.S. Court of Appeals for the District of Columbia Circuit Monday that the appeals court should force Trump to comply with subpoenas seeking information about his properties so that Congress can vote on whether or not to affirm the presidents’ right to conduct this business under the emoluments clause.

But Judges David S. Tatel and Thomas B. Griffith questioned whether these individual members of Congress had the standing to sue when it was Congress at large that was denied a vote.

“Go back, get a resolution from the House and Senate,” and then return to court, advised Griffith at one point.

The judges also pressed the Department of Justice, which is representing Trump in the case, about what options lawmakers have if not to sue. They highlighted that in other lawsuits, the Department of Justice has challenged Congress’s right to seek documents and testimony from the president to conduct oversight.

Without information needed to vote on the emoluments the president receives, should Congress impeach the president as their remedy, the judges asked. Counsel for the Department of Justice declined to take a position on whether the emoluments allegations raised against the president rise to level of impeachable offenses.

“I personally think that the scope and magnitude of the president’s ongoing defiance of the Constitution and the emoluments clause is impeachable,” said Blumenthal after the hearing. “That is not to say it has to be included in the articles of impeachment because Congress can decide that never every potential impeachable offense is included in the articles of impeachment.”

So far, House Democrats have not moved to fold Trump’s business dealings into the impeachment inquiry, although Rep. Jerrold Nadler, D-N.Y., is another top plaintiff in the lawsuit and leads the House Judiciary Committee, now overseeing the inquiry.

The Department of Justice counsel also argued that the lawmakers lacked the standing to sue and could seek other remedies like passing broad legislation prohibiting Trump from doing business with representatives of foreign countries. The attorney said it was “not plausible” that the founding fathers intended as broad a definition of emoluments as the plaintiffs are using.

The Department of Justice did not immediately respond to requests for comment after the hearing.

District Court judges have largely sided with Blumenthal and his lawyers from the Constitutional Accountability Center in the more than two years since the case was filed. But appellate judges have previously ruled in the Department of Justice’s favor by ordering the lower court to reconsider the president’s right to appeal and receive a stay on subpoenas.

President Trump has called the emoluments clause “phony.” He attempted to host a G-7 summit of world leaders at his Doral golf club in Florida this fall, but rescinded the idea after bipartisan criticism.

Media reports have found that Trump buildings in Manhattan lease office space to the governments of Afghanistan, India, Iraq, Kuwait, Qatar, Malaysia, Saudi Arabia, Slovakia, and Thailand and to a bank owned by China. Representatives from Saudi Arabia, Malaysia and Kuwait have spent thousands at his hotels.

Another case challenging the president over the emoluments clause was filed by attorneys general of Maryland and the District of Columbia, who believe Trump’s ownership of his D.C. hotel gives other venues in the District and Maryland a competitive disadvantage. Their case will be heard on Thursday in Virginia.

A third case is pending in New York, brought by Trump’s hospitality competitors.