Washington (CNN)A federal appeals court in Washington on Tuesday morning will consider some of the most significant constitutional questions the courts have ever weighed, with nine judges hearing arguments on whether former White House counsel Don McGahn must testify under congressional subpoena about President Donald Trump and whether Trump can divert billions of dollars to build a wall on the US-Mexico border.

       The historic doubleheader at the US Court of Appeals for the District of Columbia Circuit could last hours and put several notable federal judges in a position to comment on some of the President's most controversial policies. The judges are considering whether the federal courts can resolve standoffs between Congress and the executive branch, a question that, once answered, will have implications for years to come.

       The Democratic-controlled House of Representatives so far has argued how the Trump administration has thwarted it more than any other previous administration, upsetting the checks and balances on the presidency. On the other hand, the Justice Department, representing Trump and his Cabinet, has argued the courts should stay out of the disputes, letting Congress use politics and legislation to force the Trump administration into compliance if it must.

       The hearing is likely to be tough on the administration. Seven of the nine judges hearing the cases were appointed by Democrats, including Merrick Garland, the Obama Supreme Court nominee whose confirmation Senate Republicans derailed with Trump's election in 2016.

       The arguments will cover two cases: the appeal on the blocked subpoena of McGahn, whom the House sought to question about Trump's actions during the Mueller investigation, and on the Trump administration's decision to use billions of dollars more than the House intended to build the wall after calling the US-Mexico border an emergency for the Defense Department to handle.

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       The court case that could change the trajectory of the Trump administration

       The House Judiciary Committee has been trying to interview McGahn under oath since last spring, when the Mueller report came out, so it could continue to investigate Trump for obstruction of justice, even after his impeachment. The case had been a flashpoint during Trump's impeachment, because it tested the White House's successful blocking of administration witnesses during those proceedings.

       At the height of the impeachment battle, District Judge Ketanji Brown Jackson ruled McGahn must testify and the White House had no ability to claim absolute immunity to protect its current or former officials from congressional subpoenas. "Presidents are not kings," she wrote. But the order was sidelined with the appeals and impeachment ended with the Senate acquitting Trump without calling witnesses.

       In the first go-around at the appeals court, a 2-1 panel said McGahn couldn't be forced to testify. The two judges, Thomas Griffith and Karen Henderson, will also be the only Republican-appointed judges on the nine-member panel Tuesday.

       Two Trump-appointed DC Circuit judges, Neomi Rao and Greg Katsas, who along with the nine would compose the full court, will not hear the case after apparently recusing themselves.

       Border wall fight

       In the border wall case, Congress' authority to force the administration's approach came up again before the DC Circuit, regarding how the House appropriated funding to various executive agencies.

       After Congress approved $1.375 billion for border wall construction, the Trump administration declared a national emergency at the southern border, adding billions of dollars to the amount it would use for the wall.

       District Judge Trevor McFadden, a Trump appointee, last year refused to stop the administration from using the money, as the House had requested, in essence ruling for the administration.

       Trump picks controversial McConnell ally for powerful appeals court

       "Congress has several political arrows in its quiver," McFadden wrote, adding that "this lawsuit is not a last resort for the House."

       Clashes over hotly contested actions by the Trump administration have led to intense debates in court, especially over the last year. But the typical flow of arguments, especially when cases are before a full appeals court and judges can debate one another and the lawyers before them, may not be as smooth.

       No judges or lawyers will be in a courtroom on Tuesday -- instead, they'll be calling in to a teleconference because of court policy during the coronavirus pandemic.

       And the DC Circuit almost certainly won't rule on Tuesday. When the court ultimately does, whichever side loses is likely to head to the Supreme Court.

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