President Donald Trump escalated his efforts to discredit the Russia investigation Wednesday, saying the FBI has been caught in a "MAJOR spy scandal" over their use of a secret informant to determine whether some of Mr. Trump's campaign aides were working with Russia ahead of the 2016 election.

SPYGATE could be one of the biggest political scandals in history! — Donald J. Trump (@realDonaldTrump) May 23, 2018

"SPYGATE could be one of the biggest political scandals in history!" Mr. Trump said in an early morning Twitter tirade.

Mr. Trump and his GOP supporters in Congress are now demanding information on the outside informant, claiming it is proof that the Obama administration was trying to spy on his campaign for political reasons. The White House has negotiated rare access to classified documents for Mr. Trump's congressional allies in a briefing expected Thursday.

Look how things have turned around on the Criminal Deep State. They go after Phony Collusion with Russia, a made up Scam, and end up getting caught in a major SPY scandal the likes of which this country may never have seen before! What goes around, comes around! — Donald J. Trump (@realDonaldTrump) May 23, 2018

"Look how things have turned around on the Criminal Deep State," Mr. Trump tweeted Wednesday. "They go after Phony Collusion with Russia, a made up Scam, and end up getting caught in a major SPY scandal the likes of which this country may never have seen before! What goes around, comes around!"

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The president's comments came a day after he increased pressure on the Justice Department, declining to say whether he has confidence in Deputy Attorney General Rod Rosenstein. Over the weekend, Mr. Trump demanded that the Justice Department investigate the FBI and Justice Department's handling of the Russia probe.

Speaking in the Oval Office on Tuesday, Mr. Trump responded to the news that an FBI informant was in contact with members of his campaign. "That would be one of the biggest insults that anyone's ever seen," Mr. Trump said. "If they had spies in my campaign, during my campaign for political purposes, that would be unprecedented in the history of our country."

Former FBI Director James Comey responded to the presidents comments on Wednesday, tweeting that the FBI's use of informants or "Confidential Human Sources" is "tightly regulated and essential to protecting the country." He added that attacks on the agency and "lying about its work" would do "lasting damage to our country."

Facts matter. The FBI’s use of Confidential Human Sources (the actual term) is tightly regulated and essential to protecting the country. Attacks on the FBI and lying about its work will do lasting damage to our country. How will Republicans explain this to their grandchildren? — James Comey (@Comey) May 23, 2018

The Justice Department has since agreed by expanding an open, internal investigation to determine whether there was any politically motivated surveillance. Justice Department spokesperson Sarah Flores released a statement on Sunday saying that the department "has asked the Inspector General to expand the ongoing review of the FISA application process to include determining whether there was any impropriety or political motivation in how the FBI conducted its counterintelligence investigation of persons suspected of involvement with the Russian agents who interfered in the 2016 presidential election."

Her statement also said that "the Inspector General will consult with the appropriate U.S. Attorney if there is any evidence of potential criminal conduct," and it said that Rosenstein issued a statement saying, "If anyone did infiltrate or surveil participants in a presidential campaign for inappropriate purposes, we need to know about it and take appropriate action."

And the White House said that Trump chief of staff John Kelly would organize the meeting with House lawmakers to review the documents, although he and other White House staffers would not be present.

FBI Director Christopher Wray, National Intelligence Director Dan Coats and Justice Department official Edward O'Callaghan will meet with House Intelligence Committee Chairman Devin Nunes and House Oversight and Government Reform Chairman Trey Gowdy.

White House press secretary Sarah Sanders said no Democrats were invited because they had not requested the information, despite calls from lawmakers for the briefing to be bipartisan.

The top Democrat on the House intelligence panel, California Rep. Adam Schiff, said the briefing should have been done through the bipartisan "Gang of 8," which includes Republican and Democratic leaders and the top Republicans and Democrats on the House and Senate intelligence panels. That group regularly receives classified briefings.

The New York Times was the first to report that the FBI had an informant who met several times with Trump campaign officials who had suspicious contacts linked to Russia.

The Justice Department's internal probe began in March at the request of Attorney General Jeff Sessions and congressional Republicans. Sessions and the lawmakers urged Inspector General Michael Horowitz to review whether FBI and Justice Department officials abused their surveillance powers by using information compiled by Christopher Steele, a former British spy, and paid for by Democrats to justify monitoring Carter Page, a former campaign adviser to Mr. Trump.

Horowitz said his office will look at those claims as well as communications between Steele and Justice and FBI officials.