WASHINGTON — President Trump said Sunday that he would demand that the Justice Department explore whether it or the FBI “infiltrated or surveilled the Trump Campaign for Political Purposes” – perhaps signaling the start of a showdown between the nation’s chief executive and its federal law enforcement apparatus.

After several tweets railing against the year-old special counsel probe into his campaign, Trump wrote, “I hereby demand, and will do so officially tomorrow, that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes – and if any such demands or requests were made by people within the Obama Administration!”

The tweet seemed to be a response to recent reports about the FBI using a longtime intelligence asset to advance its investigation into Russian election interference. Trump and his allies have seized on the use of the asset to claim that the FBI has spied on his campaign.

The president’s demand is significant in its own right: the nation’s chief executive ordering an investigation into the investigation of his campaign. But it also could presage more important developments.

House Intelligence Committee Chairman Devin Nunes, R-Calif., has sought documents on the FBI’s use of the asset and, so far, has been rebuffed by Justice Department leaders, who worry that exposing the source or the source’s work could put him in danger. The president could order the department to hand over the materials, over its objection, potentially sparking significant backlash among top officials there and in the broader intelligence community.

Law enforcement had considered the source’s identity so sensitive that the FBI had been working over the past two weeks to mitigate the potential damage if his name was revealed, according to several people familiar with the matter. It is possible that officials could resign in protest or refuse the president’s order and force him to fire them.

But the president’s tweet also left open the possibility that such a conflict could be averted.

Justice Department Inspector General Michael Horowitz announced in March that he would explore controversial applications to surveil former Trump campaign adviser Carter Page, along with the department’s relationship with a former British intelligence officer who provided information cited for those requests. That review will assess whether the FBI and the Justice Department complied with the law and their own policies in requesting and carrying out the surveillance. Horowitz also said that he would examine other matters that might arise from his work.

It is possible that Horowitz’s work might have naturally led him to look at the FBI’s use of the confidential source, who had contact with Page, in the Russia investigation. The Justice Department also would not necessarily chafe at an internal look at its conduct.

In an interview with The Washington Post, Rudy Giuliani, the president’s attorney, said Trump was “doing what the president should do. He’s telling the Justice Department the obvious, which is – they should turn over information gleaned from this source.” But he offered less-than-clear answers on what the president’s ultimate directive would be.

Asked whether the president wanted the documents released, Giuliani responded, “Yes, he wants them released in this case to Congress.” But later in the conversation, Giuliani seemed to note that the president had not yet given a formal order. He said he expected a letter would be issued Monday.

“He’s not commanding them at this point but asking them to reveal the substance of this and clear it up,” Giuliani said. “We think that’s only fair. If they don’t do it, he’s the president, the executive branch of a government that’s being maligned. He has the right to say, ‘Straighten it out.’ ”

Giuliani said he was not worried about that sparking a possible crisis at the Justice Department, saying, “I have a hard time believing they won’t go along. They have to eventually reveal something about this. This is a serious issue.”

“They may want to put some strictures on it, like it has to be confidential, or they don’t give the name but they give the information. If they don’t want to do anything, it’s a serious problem and far worse than we even believe.”