President Trump’s threat to pursue legal action against Congresswoman Liz Cheney, “is escalating,” the Hill reports, as he suggests the former representative of Wyoming “should be prosecuted for her work” on the January 6 committee. Count us out. We have published our share of editorials excoriating the J6 committee, but it’s hard to see how Ms. Cheney can be brought to book, given the Constitution’s “Speech or Debate” clause.

That famous clause, these columns pointed out when Senator Graham faced legal questioning over the 2020 vote count, “is American bedrock” and “one of the props in our constitutional system of separated powers.” It bars, in Article I, Section 6,  the other branches from interfering with the legislature. It says of our Representatives and Senators that “for any Speech or Debate in either House, they shall not be questioned in any other Place.”

That hasn’t kept Trump from griping that “Liz Cheney has been exposed in the Interim Report, by Congress, of the J6 Unselect Committee as having done egregious and unthinkable acts of crime.” He is referring to an allegation by a House subcommittee claiming that, while the J6 panel was conducting its investigation, Ms. Cheney “improperly communicated with star witness Cassidy Hutchinson,” the Hill reports.

Ms. Hutchinson was an aide to Trump’s former chief of staff. Her testimony to the panel featured the claim that Trump had wanted to go to the Capitol on January 6, only to be thwarted by the Secret Service. The House report, written under the aegis of Congressman Barry Loudermilk, suggests that Ms. Cheney “colluded” with Ms. Hutchinson. It calls for the former congresswoman to be “investigated for potential criminal witness tampering.”

The challenge of pursuing such a charge against Ms. Cheney, though, is underscored by the Hill, which notes that it “would likely be difficult for a Trump Justice Department to successfully prosecute Cheney.” This is in part, the Hill reports, because the former aide “first reached out to Cheney.” More importantly, “any work the former member of House GOP leadership did would likely be covered by the Constitution’s Speech or Debate Clause.”

That point is echoed by one of Trump’s chief congressional tormentors, Representative Jamie Raskin. He avers that the Speech or Debate clause “insulates members in the performance of their legislative duties from prosecution and investigation outside of Congress.” Mr. Raskin adds that the clause means the “legislative function, including investigation, is completely protected” — including meetings with witnesses.

Mr. Raskin’s constitutional comprehension appears to be selective, though. He is quick to cite the Speech or Debate clause, but he and his fellow Democrats failed to follow the guardrails ordained in the Constitution against bills of attainder. That’s the prohibition on Congress to avoid what the Supreme Court called “trial by legislature,” which is more or less — meaning, precisely — what the January 6 committee sought to undertake against Trump.

In Mr. Graham’s case, the South Carolina solon faced an order to testify before a grand jury run by a Georgia district attorney, Fani Willis. Mr. Graham demurred, invoking the Speech or Debate clause. The Supreme Court found that the clause shielded Mr. Graham from questioning about his legislative work — but that other topics were fair game. He spoke to the panel in November 2022. Ms. Willis is suffering her own constitutional ailments.

As for Ms. Cheney, the Hill calls the new House report “a road map for a possible investigation” of “someone the president-elect has repeatedly said should face consequences.” Why would Trump risk disappointing voters, though, after winning the election on a vow not to pursue his opponents in court? “I’m not going to have time for retribution,” Mr. Trump pledged on the campaign trail. “And remember this, our ultimate retribution is success.”