President Trump. (Jabin Botsford/The Washington Post)

SINCE THE Watergate scandal, presidents have understood the importance of keeping a respectful distance from the Justice Department, allowing its professionals to decide whom to investigate and prosecute free from the demands of White House politics. President Trump has chafed at this arrangement, complaining that he does not have enough control over the Justice Department and that Attorney General Jeff Sessions has failed to serve as his loyal fixer. But it has been unclear how much more than fume Mr. Trump would do.

So it was worrying when Mr. Trump demanded on Sunday that the Justice Department investigate unsubstantiated claims that the FBI improperly infiltrated his 2016 campaign. Any presidential edict ordering Justice to investigate a particular matter would erode the norm that presidents do not inject politics into federal law enforcement. That Mr. Trump’s motivation is part of his war against the Russia probe of special counsel Robert S. Mueller III only makes his demand more antithetical to the nation’s tradition of independent, impartial administration of justice.

Deputy Attorney General Rod J. Rosenstein sidestepped a showdown by referring the issue to Justice Department Inspector General Michael E. Horowitz, who is already examining questions around surveillance of a former Trump staffer, instead of launching a fresh criminal probe. If Mr. Horowitz finds anything amiss, he can refer his conclusions to a U.S. attorney for further investigation and possible prosecution.

Based on facts uncovered thus far, it seems unlikely that Mr. Horowitz will do anything but waste his time. Mr. Trump and his allies have presented no evidence for their claim that law enforcement officials improperly planted a spy or surveilled the president’s 2016 campaign. On the contrary, everything we have learned suggests that a counterintelligence investigation into Russia’s election meddling was more than warranted.

As if to reinforce that judgment, more information emerged over the weekend about the Trump campaign’s many fishy contacts with foreign officials. The New York Times reported that Donald Trump Jr., the president’s eldest son, met in August 2016 with George Nader, who claimed to be an emissary from the princes ruling Saudi Arabia and the United Arab Emirates. According to the Times, “Mr. Nader explained to Donald Trump Jr. that the two princes saw the elder Mr. Trump as a strong leader who would fill the power vacuum that they believed Mr. Obama had left in the Middle East, and Mr. Nader went on to say that he and his friends would be glad to support Mr. Trump as much as they could, according to the person with knowledge of the conversation.” Meanwhile, “two people familiar with the meetings said that Trump campaign officials did not appear bothered by the idea of cooperation with foreigners.” Mr. Nader would later forge ties with Donald Trump’s son-in-law, Jared Kushner, and Michael Flynn.

The nation should not let the president distract from the questions that need answering: What did Trump campaign officials know about foreign plots to help them win, and what did they do about it? What measures is the Trump administration taking to protect future elections from foreign interference?