WASHINGTON (AP) — Amid a rush of weekend tweets taking aim at targets old and new, President Donald Trump criticized the FBI and raised questions about the special prosecutor’s investigation into Russian election meddling and possible ties to his campaign.

The Twitter storm — more than a dozen tweets Saturday and Sunday — came after his former national security adviser, Michael Flynn, pleaded guilty to lying to the FBI. In one of his messages, Trump again denied that he directed FBI Director James Comey to stop investigating Flynn.

Trump questioned the direction of the federal law enforcement agency and wrote that after Comey, whom Trump fired in May, the FBI’s reputation is “in Tatters — worst in History!” He vowed to “bring it back to greatness.” The president also retweeted a post saying new FBI Director Chris Wray “needs to clean house.”

Former Attorney General Eric Holder tweeted in response: “Nope. Not letting this go. The FBI’s reputation is not in “tatters”. It’s composed of the same dedicated men and women who have always worked there and who do a great, apolitical job. You’ll find integrity and honesty at FBI headquarters and not at 1600 Penn Ave right now.”

Trump seized on reports that a veteran FBI counterintelligence agent was removed from special prosecutor Robert Mueller’s team last summer after the discovery of an exchange of text messages that were viewed as potentially anti-Trump. The agent, Peter Strzok, had also worked on the investigation of Democrat Hillary Clinton’s use of a private email server.

Peter Carr, a spokesman for Mueller, said Mueller removed Strzok from the team “immediately upon learning of the allegations.” He would not elaborate on the nature of the accusations. The person who discussed the matter with The Associated Press was not authorized to speak about it by name and spoke on condition of anonymity.

Trump tweeted Sunday: “Tainted (no, very dishonest?) FBI ‘agent’s role in Clinton probe under review.’ Led Clinton Email probe.” In a separate tweet, he wrote: “Report: ‘ANTI-TRUMP FBI AGENT LED CLINTON EMAIL PROBE’ Now it all starts to make sense!”

Strzok’s removal almost certainly reflected a desire to insulate the investigators from any claims of political bias or favoritism. Trump and many of his supporters have at times sought to discredit the integrity of the investigation, in part by claiming a close relationship between Mueller and Comey and by pointing to political contributions to Democrats made by some lawyers on the team.