WASHINGTON — The entire federal appeals court in Washington said on Friday that it would take up two cases that raised the question of whether and when Congress may sue to resolve a dispute with the president, setting up a double-barreled test for establishing when the judicial branch can resolve disputes over separation of powers.
In a terse order, the full appeals court said it would rehear a case involving a House Judiciary Committee subpoena to Donald F. McGahn II, President Trump’s former White House counsel, vacating a 2-1 panel ruling last month that Congress could not sue to enforce its subpoenas of executive branch officials.
The full court also said it would immediately take up a case that House Democrats brought against Treasury Secretary Steven Mnuchin challenging the administration’s use of emergency powers and other extraordinary measures to spend more taxpayer funds on Mr. Trump’s border wall with Mexico than Congress had been willing to appropriate.
In the border wall case, a United States District Court judge had sided with Mr. Trump and dismissed the case, saying the House had no standing to bring it. An appeals court panel heard arguments in the case weeks ago but has not yet issued a ruling. The order said that the panel had requested that the full court hear that case since it also raised an issue of standing.
The full Court of Appeals for the District of Columbia Circuit will hear arguments in both cases on April 28.
The cases raise major issues about the scope of the power of Congress to enlist the courts’ aid when lawmakers believe a president is illegally spending funds — defying its constitutional power of the purse — or instructing an aide to illegally ignore a subpoena, defying its constitutional power to conduct oversight of the government.
The McGahn subpoena case is particularly important because it could have far-reaching consequences for executive branch secrecy powers long after Mr. Trump leaves office. The now-vacated panel ruling dealt a severe blow to Congress’s ability to conduct oversight when a president is willing to simply stonewall “all” subpoenas, as Mr. Trump has vowed to do.
Mr. McGahn was a key witness in the second volume of the report by the special counsel, Robert S. Mueller III, about Mr. Trump’s efforts to obstruct the Russia inquiry. The House wanted to question Mr. McGahn about the same topic.
But on Mr. Trump’s instructions, Mr. McGahn defied the House subpoena. The House sued him, seeking a judicial order that he show up to testify, and won in district court in November.
The Justice Department filed an appeal, and last month, two of the three appeals court judges on the panel ruled that the Constitution gave the House no standing to file any such lawsuit in what they characterized as a political dispute with the executive branch — a ruling that, if it stood, would cripple the ability of Congress to investigate current and future presidents.
Normally, panels of three judges decide disputes that come before federal appeals courts. But litigants who lose at the panel level can choose to appeal to the entire body to have the case reheard. That can be important when the ideological balance between the three-judge panel and the full court is different.
The scope of Congress’s power to conduct oversight and seek judicial redress in disputes with the president has no fixed partisan implications; both major parties trade control of both branches, so sometimes a Republican Congress will be battling a Democratic president.
But so far, both cases have followed a pattern at both the district and appellate levels. Every judge who sided with Mr. Trump was a Republican appointee, and every judge who sided with Congress was a Democratic appointee. (In similar cases in the past, however, district court judges have sided against presidents of the same party of the president who appointed them.)
Notably, the partisan balance on the full appeals court cuts the other way: Seven of the 11 active judges were appointed by Democratic presidents.
Still, should the full appeals court determine that the House does have standing to bring the lawsuit and order Mr. McGahn to testify, the Justice Department could again appeal to the Supreme Court. There, five of the nine justices are conservative Republican appointees.
Depending on how long the case takes to resolve, the presidential election may take place in the interim. In 2008 and 2009, a similar dispute over whether a former White House lawyer for President George W. Bush, Harriet Miers, had to testify in response to a subpoena was resolved without further litigation after Barack Obama succeeded Mr. Bush as president.