It would harm the executive branch they say but what they mean is it would harm THEIR executive branch.

This was done during Nixon's impeachment.

https://www.nytimes.com/2020/05/07/us/politics/mueller-supreme-court.html

WASHINGTON — The Trump administration asked the Supreme Court on Thursday to block Congress from seeing grand jury secrets gathered in the Russia investigation by the special counsel, Robert S. Mueller III, saying the executive branch would suffer irreparable harm if lawmakers see the evidence.

In a 35-page filing, Noel J. Francisco, the solicitor general, asked the justices to halt an order by a federal appeals court that imposed a May 11 deadline on the Justice Department to turn over the evidence to the House Judiciary Committee. He said the Justice Department should first get a chance to fully litigate an appeal of the ruling before the Supreme Court.

“The government will suffer irreparable harm absent a stay. Once the government discloses the secret grand-jury records, their secrecy will irrevocably be lost,” Mr. Francisco wrote, adding, “That is particularly so when, as here, they are disclosed to a congressional committee and its staff.”

House Democrats have argued that they need to see the grand jury evidence in part because of suspicions that Mr. Trump may have lied under oath in his written answers to Mr. Mueller, including about his campaign’s advance knowledge of and contacts with WikiLeaks about its possession of hacked Democratic emails and plans to publish them.

But under Attorney General William P. Barr, the Justice Department has fought to prevent House investigators from seeing the grand-jury material, including information that was blacked out in the report on the Mueller investigation it released last year and underlying testimony transcripts those passages derived from.

Usually, Congress has no right to view grand jury evidence. But in 1974, the courts permitted lawmakers to see such materials as they weighed whether to impeach President Richard M. Nixon. Last summer, as the House Judiciary Committee weighed whether to impeach President Trump, it sought a judicial order to see certain Mueller grand jury materials, too.


The politically charged fight turns on a technical legal issue: whether the impeachment process, which begins with a House inquiry and can culminate in a Senate trial, counts as a “judicial proceeding” under an exception to grand-jury secrecy rules that permits sharing evidence for that purpose.

Both a Federal District Court judge ruled last fall, and a panel of the Court of Appeals for the District of Columbia ruled this spring, that impeachment is a judicial proceeding, following the Nixon impeachment precedent. But the Trump administration has delayed any sharing of the evidence by continuing to argue at each level that it is not.

In the request to the Supreme Court that it halt the appeals court’s order that the Justice Department turn over the material by May 11, Mr. Francisco argued that “at least four justices” — the number necessary to take an appeal — are likely to decide that the Supreme Court should weigh in on the issue, and that “there is at least a fair prospect” that a majority will eventually rule in favor of Mr. Trump.

But if the House has already seen the evidence in the interim, he argued, the executive branch will be harmed even if it ultimately wins the case. He noted that nothing could stop House Democrats from publicly releasing the evidence Mr. Mueller gathered by a simple-majority vote in the Judiciary Committee.