It seems Mr. Trump himself directed Mr. Flynn to make contact with the Russians.

If Mr. Flynn testifies to this — ABC’s Brian Ross is reporting that he will — it presents another impeachable offense along with the possible obstruction of justice. Even more, it brings the whole matter well outside the purview of the criminal courts into the province of a political scandal, indicating abuses of power arguably well beyond those in the Watergate and Iran-contra affairs.

Mr. Flynn asked Russia to intervene at the United Nations on behalf of Israel.

He is admitting that last Dec. 22, he asked Mr. Kislyak to delay or defeat a United Nations Security Council resolution condemning Israel for its settlement policy, which the Obama administration had decided to let pass. The possible involvement or knowledge of Israel in the case will be one of many questions that congressional investigators will pursue.

The lying is bad. Conducting rogue American foreign policy is worse.

In the end, Mr. Flynn’s lies are secondary to the demonstration that the Trump administration was actively undermining American foreign policy before it took office. This will most likely prove the most abiding scandalous fact of the Mueller investigation. And it’s one that nobody on either side of the aisle could possibly defend.

Mr. Flynn’s cooperation portends extreme peril for a variety of people in the president’s orbit.

Most immediately vulnerable? Jared Kushner. Mr. Flynn was present at a Dec. 1, 2016, Trump Tower meeting where Mr. Kushner is said to have proposed to Mr. Kislyak setting up a back channel for the transition team to communicate with Moscow.

Those and related details are now front and center in the investigation. Criminal liability aside, Friday’s news — including a report that Mr. Kushner was the one who directed Mr. Flynn to contact Russia — helps cement Mr. Kushner’s reputation as a callow and arrogant freelancer, authorized by the president to act way over his head, and possibly impairing some of the most delicate and important issues of foreign policy. (A possible winner, on the other hand, is the younger Mike Flynn, about whose criminal liability his father was extremely concerned. Look to see how Mr. Mueller now chooses to treat the younger Mr. Flynn, who is being investigated over his work for his father’s lobbying business.)

Mr. Flynn’s plea raises the likelihood that he will give testimony in support of a potential obstruction of justice charge against Mr. Trump.

The basis for the possible obstruction charge against the president has been his efforts to get the F.B.I. director, James Comey, to shut down the Flynn investigation during a Feb. 14 meeting in the Oval Office, coupled with his multiple lies on the subject. Obstruction is plainly an impeachable offense: It’s the offense for which Richard Nixon was threatened with impeachment.

For months, it has seemed the possible culminating charge of the Mueller investigation, a straightforward and readily understandable high crime or misdemeanor. Such a charge, per Department of Justice policy, would not be brought in the criminal courts but would rather form the basis of a report to Congress potentially recommending impeachment. If Mr. Mueller brings that charge, it will be on the strength of Mr. Flynn’s testimony.

Mr. Trump’s defenders have fewer and fewer cards to play.

There had been a prospect that the obstruction of justice charge, if it did come, would be dismissed by die-hard Trump supporters as subject to conflicting interpretations of Mr. Trump’s state of mind, and therefore not deserving of impeachment or removal. No longer. Now Mr. Trump and his circle will stand accused by a former member of the administration with plainly unconstitutional meddling in the most sensitive of foreign policy issues. If the Congress and country believe Michael Flynn’s account, it is hard to see what even the staunchest Trump defenders can say in defense. That means that as Mr. Trump and the administration look out at the new landscape featuring a guilty Michael Flynn, it’s kill or be killed.