A federal appeals court in Washington, D.C. on Tuesday heard arguments over a Democratic challenge to the Trump administration’s use of defense funding to build a wall along the U.S.-Mexico border.

The House Democrats’ lawsuit arose early last year after President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE declared a national emergency at the southern border. Trump’s move sought to free up additional funding after a congressional spending bill allocated some $1.3 billion for border security, far short of the nearly $5 billion Trump said was needed to complete his signature project.

Lawmakers allege that Trump’s diversion of defense, military and other funding — billions of dollars that were not specifically earmarked for border wall construction — violated the Appropriations Clause of the Constitution, which gives Congress the exclusive power of the purse.

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The argument on Tuesday before the U.S. Court of Appeals for the D.C. Circuit centered on a key procedural question: whether the court has the power to referee the fight between Congress and the White House or if the dispute should be left to the political process.

The circuit court bench that presided over Tuesday's argument was composed of seven judges appointed by Democrats and two Republican appointees.

With in-person court activity curtailed amid the public health crisis, the border wall funding case was argued over a livestreamed conference call. Arguments in that case were consolidated with a dispute about Congress’s power to subpoena former White House counsel Don McGahn over White House objections that raised similar procedural questions.

Douglas Letter, a lawyer for the House, urged the court to reach a narrow ruling on the border wall case that avoided upsetting the separation of powers but upheld the Framers’ view that the Constitution aims to stop “a monarch from spending freely.”

“Litigation has proven to be a tried and true mechanism by which the courts have resolved constitutional disputes between Congress and the president on many occasions,” Letter said. “There is no good reason to abandon this here.”

The Justice Department, on behalf of the Trump administration, argued that the border wall funding fight is “the type of dispute that is committed to the political branches.”

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“That doesn't mean we resort to revolution, because Congress in the political branches has ample tools,” said Justice Department lawyer Hashim Mooppan, noting that lawmakers could respond with funding cuts or by holding up presidential nominees.

Robert Tsai, a law professor at American University, said the court faces a tough decision, but a win for the Trump administration would reduce the House's leverage.

“If the D.C. Circuit holds that the House cannot sue, that institution will lose an important stick in its bundle to force a president to negotiate a resolution over appropriations," Tsai said. "During our polarized time, explicitly overturning a president’s reallocation decision over a veto is nearly impossible to accomplish."

"On the other hand, getting between Congress and a president over funding battles raises genuine separation of powers concerns, and courts have often preferred to let the political branches duke them out," he added.

The case is one of several lawsuits filed against the Trump administration over its emergency border wall funding, some of which were brought by private parties.

In June, a federal judge in D.C. rejected House Democrats’ request to block the administration from transferring funds from the departments of Defense and Treasury toward the border wall. U.S. District Judge Trevor McFadden, a Trump appointee, said the court lacked the power to intervene, prompting the appeal.

“While the Constitution bestows upon Members of the House many powers, it does not grant them standing to hale the Executive Branch into court claiming a dilution of Congress’s legislative authority,” McFadden wrote in a 24-page decision. “The Court therefore lacks jurisdiction to hear the House’s claims and will deny its motion.”

The Supreme Court last July ruled 5-4 that Trump could begin spending $2.5 billion in reallocated Pentagon funds to build the border wall while the legal challenges proceeded through the courts.

The case before the D.C. circuit court is U.S. House of Representatives v. Steven T. Mnuchin.

--This report was updated at 1:42 p.m.