Rich Lowry of National Review Online takes aim at the nation’s leading law-enforcement agency.

The FBI took it upon itself to determine whether the president of the United States is a threat to national security.

No one had ever before thought that this was an appropriate role for the FBI, a subordinate agency in the executive branch, but Donald Trump isn’t the only one in Washington trampling norms.

The New York Times reported the astonishing news. “Counterintelligence investigators,” the paper writes, “had to consider whether the president’s own actions constituted a possible threat to national security.” U.S. presidents over the decades have made many foolhardy decisions that have undermined our security; never before have they been deemed a fit subject for an FBI investigation.

The proximate cause for the probe into Trump was his firing of FBI director James Comey, which the FBI considered both a potential crime and a national-security matter because it might shut down the investigation into Russian efforts to influence the 2016 election. …

… As part of the executive branch, the FBI should brush up on the powers of the chief executive. The president gets to fire subordinate executive-branch officials. He gets to meet with and talk to foreign leaders. He gets to make policy toward foreign nations. Especially important to the current investigation, he gets to say foolish, ill-informed, and destructive things.

If the president wants to tilt toward Russia (not that Trump really has, except in his words), he can. If he wants to butter up China’s dictatorial president during high-stakes trade negotiations, he can. If he wants to announce a precipitous withdrawal from Syria and make it slightly less precipitous in a fog of confusion, he can.

And the FBI should have nothing to say about it.