President Trump is using the Justice Department in unprecedented, partisan ways and asserting ludicrously aggressive and unprecedented claims of executive power. The question is whether — in some cases, at least — the courts will stop him.

The Justice Department these days is tool of partisan vengeance for this administration. Attorney General William P. Barr opened what is the third investigation into the origins of the Russia probe. (Hmm, Russia interfering with our election, maybe?) Not only do we know this from the hearings to date (George Papadopoulos was overheard talking about getting dirt from Russians on Hillary Clinton), but the notion that this was all a nefarious plot would mean that former deputy attorney general Rod J. Rosenstein (a Trump Republican appointee who signed off in FISA warrants) was in on it as well as three separate FISA judges and legions of career officials at Justice, the CIA and elsewhere in the intelligence community. And the plot was so diabolical that they all kept the Trump campaign’s cozy relationship with Russians a secret throughout the election. The “theory” (more like a nonverbal impulse) of this noncase is preposterous. And yet Barr has assigned a prosecutor to it.

Meanwhile, Trump’s lawyers are demanding a reprieve from discovery in the emoluments case while they take up an interlocutory appeal.

The president has also ordered the Treasury Department to ignore the plain words of the statute requiring the IRS to turn over tax returns to the chairman of the House Ways and Means Committee.

Trump’s lawyers also groused, “This case presents the unprecedented circumstance of impending civil discovery against the sitting President of the United States concerning his compliance with a constitutional provision in his official capacity. Any discovery would necessarily be a distraction to the President’s performance of his constitutional duties.” Umm, Paula Jones, anyone? That excuse about interfering with the president’s duties was rejected more than 20 years ago.

The most important case of all is, ironically, one that Trump brought seeking to block Congress from obtaining his financial records from the accounting firm Mazars USA. Trump’s lawyers actually asserted that Congress has no oversight role in examining corruption, conflicts of interest or any other matter. The Justice Department can do it, they argue (!). All Congress can do is pass bills.

U.S. District Judge Amit P. Mehta seemed stunned. The Post reports:

“Is it your position that whether the president has properly reported his finances [under federal disclosure laws], that’s not subject to investigation by Congress?” Mehta asked.

You see, nothing — certainly not Congress — can “interfere” with the president. That’s precisely what the Framers rejected in drafting the Constitution. Interference is nothing more than checks and balances.

“Consovoy’s arguments on behalf of Trump, seeking to block private entities from turning over documents and information needed by Congress to perform its Article I functions, are so preposterous that Judge Mehta had no choice but to resist them,” constitutional scholar Laurence Tribe told me. “For the district court to accept those arguments would be astonishing — an unthinkable loss for the separation of powers. For the district court to reject those Trump arguments, as I expect it to do, will be an unsurprising win — a big victory but too predictable to count as a game-changer.”

By making an argument that virtually writes Congress out of the equation, Trump’s lawyers may have set him up for a rude awakening on the subject of separation of powers. As Tribe put it, “It’ll be a self-inflicted wound suffered by Team Trump.”

Ominously for Trump and his stonewalling lackeys, Mehta observed, “There’s not a single Supreme Court or appellate case since 1880 that has found Congress overstepped its legislative authority by issuing a subpoena.” Oops.

Former federal prosecutor Joyce Vance White told me, “Trump’s notion that Congress has no ability to investigate misconduct by a President in order to fulfill its constitutional obligations is nonsensical.” She continued, “I would expect Judge Mehta to look at the issues in a serious, thoughtful manner and to rule consistent with the law, which is going to be bad news for the President.”

Several caveats should be kept in mind. First, it’s risky to read too much into a court’s questions. Second, Mehta’s ruling would probably be appealed. And finally, Mehta’s ruling would not apply to other cases, just this one. Nevertheless, Mehta could strike a blow against Trump’s unconstitutional accretion of power and imperial pretensions by slapping him down with a broadly worded opinion on the role of congressional oversight. Finally, someone may stand up to Trump and stop him (even in one case) in his tracks.

Read more:

Greg Sargent: As Trump blunders towards war with Iran, Adam Schiff sounds the alarm

Max Boot: The dirty little secret of the ‘Trump Doctrine’: There isn’t one

Jennifer Rubin: The best retort to ‘The election’s too important to nominate a woman’

David Byler: Religiously unaffiliated voters are leading U.S. politics into uncharted waters

Dana Milbank: Trump’s not claiming executive power. He’s going for divine right.