President Trump took to Twitter the day after Christmas to say the FBI used a “bogus” dossier as the basis for investigating his campaign.

“WOW, @foxandfrlends “Dossier is bogus. Clinton Campaign, DNC funded Dossier. FBI CANNOT (after all of this time) VERIFY CLAIMS IN DOSSIER OF RUSSIA/TRUMP COLLUSION. FBI TAINTED.” And they used this Crooked Hillary pile of garbage as the basis for going after the Trump Campaign!” the president tweeted early Tuesday.

The 35-page document compiled by former British intelligence officer Christopher Steele contained salacious and mostly unverified allegations detailing Trump’s ties to Russia. It has been reported that the FBI used parts of the dossier to start its investigation into the Trump campaign.

Both Hillary Clinton’s campaign and the Democratic National Committee reportedly helped fund some of the research that ultimately became the Steele dossier.

FBI Deputy Director Andrew McCabe was grilled last week on Capitol Hill about how the dossier was used by the FBI.

Rep. Jim Jordan, R-Ohio, has wondered if the FBI used the dossier as its basis to get a Foreign Intelligence Surveillance Act warrant to surveil the Trump campaign during the 2016 presidential election. Jordan has also repeatedly asked the FBI who brought the FISA warrant application to the secret federal court that approves them.

Trump has long criticized the dossier and its alleged role in the FBI investigation. The president’s Twitter attacks on the FBI have intensified in recent months, questioning bias in its leadership and if it let Clinton off easily in its investigation into her private email server. Trump has called on the FBI and Justice Department to renew investigations into Clinton.

Meanwhile, Republicans’ claim of bias atop the FBI have gotten new life following the release of anti-Trump text messages sent between Peter Strzok, who was removed from the Russia probe by special counsel Robert Mueller, and FBI lawyer Lisa Page.

The Washington Post reported McCabe will retire in early 2018 amid criticism from Republicans.

House Republicans are also scrutinizing contacts between James Baker, the FBI’s general counsel, and Mother Jones reporter David Corn, who was the first to report on the existence of the dossier. Baker has reportedly been reassigned within the FBI, though the reason for the move is unclear.