Former CIA Director John Brennan says Donald Trump s oft-repeated claims of no collusion with Russians in the 2016 presidential election are hogwash.

Brennan hit back at the president in an editorial published in The New York Times on Thursday, a day after Trump revoked his security clearance for erratic conduct and behavior.

The only questions that remain are whether the collusion that took place constituted criminally liable conspiracy, whether obstruction of justice occurred to cover up any collusion or conspiracy, and how many members of Trump Incorporated attempted to defraud the government by laundering and concealing the movement of money into their pockets, Brennan wrote.

Russian denials of interference in the election, Brennan added, also were hogwash.

Brennan, who left his job in January 2017, said he had deep insight into Russian activities during the 2016 election.

I now am aware thanks to the reporting of an open and free press of many more of the highly suspicious dalliances of some American citizens with people affiliated with the Russian intelligence services, he wrote.

Brennan concluded: Mr. Trump clearly has become more desperate to protect himself and those close to him, which is why he made the politically motivated decision to revoke my security clearance in an attempt to scare into silence others who might dare to challenge him.

He urged that special counsel Robert Mueller be allowed to complete his investigation without interference.

Brennans editorial was published after he vowed in a series of tweets overnight to continue to criticize Trump. This action is part of a broader effort by Mr. Trump to suppress freedom of speech & punish critics, he wrote in a tweet.

The Wall Street Journal on Wednesday reported that Brennan is one of the people Trump holds responsible for what he calls the rigged witch hunt investigation into Russian interference in the 2016 election. According to the paper, Trump drew a direct connection between the probe and his decision to revoke Brennans clearance.

White House press secretary Sarah Huckabee Sanders said the president is also looking to revoke security clearances for former FBI Deputy Director Andrew McCabe, former FBI Director James Comey, former U.S. Deputy Attorney General Sally Yates, former Director of National Intelligence James Clapper and former FBI Special Agent Peter Strzok.

This article has been updated to include The Wall Street Journal report.