Legal experts say the fight over whether White House counsel Don McGahn must testify under subpoena before Congress could be settled at the Senate impeachment trial before it finishes its path through the courts.

A federal judge on Monday ruled against the Trump administration, deciding that McGahn must comply with a House Judiciary Committee subpoena seeking his testimony.

The ruling is being appealed, but Democrats could look to secure testimony from McGahn and other key witnesses directly at the Senate trial, where Chief Justice John Roberts would preside, experts said. There, Roberts would have a key role in deciding questions about admitting evidence before the case even gets to the Supreme Court.

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“It is more likely than not that the witness testimony sought from key players like McGahn and [former national security adviser] John Bolton John BoltonJudge appears skeptical of Bolton's defense of publishing book without White House approval Maximum pressure is keeping US troops in Iraq and Syria Woodward book trails Bolton, Mary Trump in first-week sales MORE will only be secured, if at all, in a Senate trial,” said Brad Moss, a national security lawyer. “Last night’s ruling would certainly provide Chief Justice Roberts with a firmer foundational footing to compel the testimony.”

House Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffSchiff to subpoena top DHS official, alleges whistleblower deposition is being stonewalled Schiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power MORE (D-Calif.) opened the door to this scenario during an interview Sunday on CNN.

“I think there's certainly merit to the idea that we may get a quicker ruling from a chief justice in a Senate trial, if it ever came to that, than we would get by going months and months on end litigating the matter,” he said. “There's no guarantee of that, but I think that it's entirely possible.”

An aide to Schiff declined to say whether the ruling against McGahn changed the chairman’s views. But some legal experts told The Hill it made the strategy more probable.

“If anything, the McGahn ruling makes it more likely it will go this way,” said Kel McClanahan, a national security lawyer.

The Constitution is silent on the rules and procedures governing a presidential impeachment, but Roberts’s dual-hatted role is spelled out. The Constitution states that the U.S. House of Representatives "shall have the sole Power of Impeachment" and the Senate "shall have the sole Power to try all Impeachments." And when the president is on trial, "the Chief Justice shall preside."

Under the Senate's rules on impeachment, written in 1986, Roberts, a George W. Bush appointee, would be expected to decide on issuing subpoenas for the Senate trial. His decisions, though, could be overruled by a majority of the chamber.

He would also rule on any objections raised by witnesses, including an assertion of “absolute immunity,” which Trump has claimed in McGahn’s case, said Charles Tiefer, a University of Baltimore law professor.

And just as U.S. District Judge Ketanji Brown Jackson, an Obama appointee, did in her Monday ruling, Roberts also could reject the Trump administration's immunity claim.

“Roberts has the stature that he could rule in favor of the Democrats on calling [White House acting chief of staff] Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE or John Bolton or [Secretary of State] Mike Pompeo Michael (Mike) Richard PompeoWatchdog confirms State Dept. canceled award for journalist who criticized Trump Trump's push for win with Sudan amps up pressure on Congress Putin nominated for Nobel Peace Prize MORE, and the Senate Republicans, who would have the option of voting to overrule him by majority vote, might let Roberts’s ruling stand,” Tiefer said.

Some legal experts believe House Democrats’ decision not to issue subpoenas to key witnesses like Bolton was strategic. The theory holds that Democrats are opting for a quick evidentiary ruling from Roberts at the impeachment trial as a much faster path to securing critical testimony than protracted court battles.

But other experts said it would be a risky move, one that could falter in the face of opposition from Republicans, who control the Senate. Under the impeachment trial rules, a majority of senators can overrule Roberts.

“Technically, the Senate sets its own rules, including evidentiary ones, and has the power to reject the presiding officer's rulings by majority vote,” said Mark Tushnet, a professor at Harvard Law School.

He added that there’s no guarantee Roberts would be willing to go along with Democrats’ requests for witnesses, even in light of Monday’s ruling against the Trump administration.

“The McGahn ruling won't matter one way or the other, except to the extent that Roberts finds its reasoning persuasive,” Tushnet said. “And it may be worth noting that Judge Brown Jackson has a pretty good reputation as a careful — though of course liberal — judge.”

Asking Roberts at the Senate trial to compel testimony from uncooperative witnesses carries other risks too. For one, Democrats do not know what those witnesses will say.

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“There is a tried and true rule for litigators," said James Robenalt, an attorney at Thompson Hine and creator of a continuing legal education class on Watergate. "Never ask a witness a question that you don’t know the answer to.”

Barbara McQuade, a law professor at the University of Michigan and a former federal prosecutor, said Democrats could simply decide the potential risks outweigh the evidentiary benefit.

“Someone like Bolton is unlikely to deliver a smoking gun beyond what we already know and may even spin his testimony in ways that are favorable to Trump,” she said. “In light of these risks, I think the House Democrats would resort to this strategy only as a last desperate resort.”

Democrats will have to decide if the political risk of the move is worth it, in particular if Republicans use the same approach.

“They [Senate Republicans] will be under pressure from Trump to call witnesses he favors, like [former Vice President Joe] Biden's son Hunter, and the whistleblower if he has been publicly identified by then,” said Tiefer, of the University of Baltimore.

“To give the president some of what he wants, Senate Republicans might take the public stance that if the Democrats have witnesses to call, so do Republicans,” he added.

Such actions from both parties are likely to put Roberts in a difficult spot.

“It would be left to Roberts to draw some lines,” Tiefer said.