Deputy Attorney General Rod Rosenstein said in a statement: "If anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action".
"This claim by the president and the suggestion by Giuliani that there is a political spy embedded in the Trump campaign is nonsense and you hear it in the same terms that Trump often speaks which is "people are saying, ' or" I'm hearing, ' or 'we're being told, ' he said". It's now folding Trump's demand into that investigation.
Nunes, who has repeatedly been blamed by Democrats for being the leaker, was referring to reports by the New York Times and the Washington Post, describing the informant as someone who supposedly had contacts with members of President Trump's campaign.
He noted that Trump was "openly mocked" when he alleged that the Obama administration placed his campaign under surveillance.
There was speculation from United States media commentators that Mr Trump's demand was an attempt to force senior justice officials into resigning.
A source familiar with the probe called the September 1 deadline "entirely made-up" and "another apparent effort to pressure the special counsel to hasten the end of his work".
A number of those charges were related to Russia's alleged interference in the 2016 election, but none of them has been extended to collusion allegations. He had come under fire for his decision to go to the White House grounds and look at classified information that suggested the Trump transition team may have been under indirect surveillance.
The special counsel's office did not respond to a request for comment.
With the demand, Trump entered into the realm of applying presidential pressure on the Justice Department regarding an investigation into his own campaign - a move few of his predecessors have made.
But former Trump adviser Steve Cortes told CNN that Papadopoulos was a "deeply irrelevant figure" in the campaign.
Neither Trump nor Rudy Giuliani, a former NY mayor who is now one of Trump's lawyers, provided any evidence of government infiltration into Trump's presidential campaign.
Trump's extraordinary demand of the Justice Department alarmed many observers, who felt it not only violated presidential protocol but could have a chilling effect on federal law enforcement or its use of informants. Trump allies from Kellyanne Conway to Rudy Giuliani were soon sharing grave concerns about the presence of a spy in the campaign's midst.
"As the president's lawyer, I can't be concerned on what effect it may have", he said.
The inspector general is being asked to determine "whether there was any impropriety or political motivation" on the part of U.S. agents who conducted counter-intelligence operations of "persons suspected of involvement with the Russian agents who interfered in the 2016 presidential election".
"We're not going to go to another meeting where we don't get documents, and then the meeting leaks out", the California Republican said during an interview on Fox News' "Sunday Morning Futures" with Maria Bartiromo.
Yet such is Trump's fury over the whole affair, it's also conceivable that his volcanic temperament and belief that he is being unfairly targeted is causing him to act in a way that raises suspicions.