President Trump on Sunday demanded that the Justice Department open an investigation into whether the department or the F.B.I. “infiltrated or surveilled” his campaign at the behest of the Obama administration, following through on his frequent threats to use his own government to target his political opponents.

Mr. Trump made the order on Twitter during a day of public venting about the special counsel investigation, which he charged had turned up no evidence of collusion with Russia and was now casting a worldwide net so that it could harm Republicans’ chances in midterm congressional elections this fall.

But in ordering up a new inquiry, Mr. Trump went beyond his usual tactics of suggesting wrongdoing and political bias by those investigating him, and crossed over into applying overt presidential pressure on the Justice Department to do his bidding, an extraordinary realm where past presidents have rarely tread.

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