So Rachel Maddow is now the voice of moderation on Donald Trump. Of course, it’s only by comparison to John Brennan. In an interview Friday on MSNBC, Ms. Maddow gently intimated that the former Central Intelligence Agency director might have gone too far in calling the president “nothing short of treasonous” for his Helsinki press conference with Vladimir Putin. Mr. Brennan backed away—but just a little.

“I didn’t mean that he committed treason,” Mr. Brennan said. Ms. Maddow pressed him, noting that treason is a “serious allegation” and saying “if we diagram the sentence, ‘nothing short of treasonous’ means it’s treason.”

By Sunday’s appearance on NBC’s “Meet the Press,” Mr. Brennan had shaken loose any qualifiers. When asked if he regretted his words, Mr. Brennan replied, “I called his behavior treasonous, which is to betray one’s trust and to aid and abet the enemy. And I stand very much by that claim.”

Mr. Trump’s decision last week to revoke Mr. Brennan’s security clearance drew predictable howls from the president’s opponents—and equally predictable defenses from his supporters. But the most interesting response has been from Brennan allies warning him that his intemperance may be backfiring.

Start with his colleague in the Obama administration’s intelligence community, James Clapper. Though the former director of national intelligence excoriated the president for stripping Mr. Brennan of his clearance, he also admitted on CNN this Sunday that “John and his rhetoric have become an issue in and of itself.” Message to Mr. Brennan: Shut your mouth, John, because you are doing more harm than good.

Mr. Clapper had plenty of company. Retired Adm. Mike Mullen, a former chairman of the Joint Chiefs of Staff, likened Mr. Trump’s plan to strip critics of clearances to Nixon’s enemies list. But he went on to say that Mr. Brennan’s over-the-top charges have “put him in a political place which actually does more damage for the intelligence community.”

Finally, there’s Sen. Richard Burr, the Republican chairman of the Senate Intelligence Committee. Mr. Burr has defended the intelligence community’s conclusion that Russia intervened in the 2016 election to help Mr. Trump win. Yet in a statement released last Thursday, he slammed Mr. Brennan for writing a New York Times op-ed that accused the president’s campaign team, without evidence, of having colluded with the Russians.

“If Director Brennan’s statement is based on intelligence he received while still leading the CIA,” Mr. Burr wrote, “why didn’t he include it in the Intelligence Community Assessment released in 2017? If his statement is based on intelligence he has seen since leaving office, it constitutes an intelligence breach. If he has some other personal knowledge of or evidence of collusion, it should be disclosed to the Special Counsel, not The New York Times.”

Mr. Brennan has responded to all this by threatening to sue the president. It is almost certainly a hollow threat. In addition to having a doubtful legal case, a lawsuit would give the president’s team an opening for some uncomfortable discovery about Mr. Brennan’s behavior.

Just one example of a question that might be difficult to answer under oath: When you were CIA director, did you ever speak directly to the press, or ask someone else to speak to the press, about matters pertaining to the Russia investigation with the condition that you were not named as a source? If so, whom did you speak to and what information did you convey?

On Monday Mr. Trump tweeted his own response to the threat of a suit: Bring it on. “I hope John Brennan, the worst CIA Director in our country’s history, brings a lawsuit,” he wrote. “It will then be very easy to get all of his records, texts, emails and documents to show not only the poor job he did, but how he was involved with the Mueller Rigged Witch Hunt.”

Plainly Mr. Brennan’s decision to put himself out in front of the Trump resistance is giving his more thoughtful allies heartburn. He doesn’t seem to appreciate what Messrs. Clapper and Mullen surely do: that the unhinged and highly politicized attacks he’s been directing at Donald Trump after stepping down as CIA director may inadvertently be helping to advance the case that he was equally politicized while on the job.

In the end, the heat and drama over revoking security clearances for former government officials is but a proxy for a larger battle. Thus far the best take has been offered by George W. Bush’s former press secretary, Ari Fleischer. In a recent tweet Mr. Fleischer says that while he doesn’t like the politics of retaliation, “it’s worth pointing out that outgoing Obama officials retaliated against Trump because he won the election”—and that they did their dirty work in the dark.

“Someone leaked to CNN about the dossier briefing and someone unmasked [Mike] Flynn,” tweets Mr. Fleischer. “Trump does his retaliating openly. Obama officials hid their retaliation, and the MSM fell for it.”

Write to mcgurn@wsj.com.