WASHINGTON >> President Donald Trump escalated his efforts to discredit the Russia investigation today, saying the FBI has been caught in a “MAJOR spy scandal” over its use of a secret informant to determine whether some of Trump’s campaign aides were working with Russia ahead of the 2016 election.

“SPYGATE could be one of the biggest political scandals in history!” Trump tweeted.

Former FBI Director James Comey, who was fired by Trump last year, said the agency’s use of secret informants was “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?” tweeted Comey, a former Republican who now identifies as an independent.

At issue are reports that a longtime U.S. government informant approached members of Trump’s campaign in a possible bid to glean intelligence on Russian efforts to sway the election.

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

“Look how things have turned around on the Criminal Deep State,” Trump tweeted today. “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!”

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, Trump demanded that the Justice Department investigate the FBI and Justice Department’s handling of the Russia probe.

The Justice Department agreed by expanding an open, internal investigation to determine whether there was any politically motivated surveillance. 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 Trump.

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