Trump brings out the knives in his effort to derail the FBI-Mueller investigation into Russian involvment in his presidential campaign

What occurred.....

Andrew McCabe became acting head of the US Federal Bureau of Investigation (FBI) after the sudden firing of James B. Comey on 9 May 2017 and, as acting head gave evidence before a US Senate committee in which he contradicted the WhiteHouse’s assertion that James B. Comey, the F.B.I. director fired by PresidentTrump...had lost the support of rank-and-file F.B.I. agents.

US President Donald Trump's reaction was hostile across multiple tweets over the following months and he implied that McCabe might be fired before he could retire.  

On 15 March 2018 The New York Times reported:

WASHINGTON — The special counsel, Robert S. Mueller III, has subpoenaed the Trump Organization in recent weeks to turn over documents, including some related to Russia, according to two people briefed on the matter. The order is the first known instance of the special counsel demanding records directly related to President Trump’s businesses, bringing the investigation closer to the president.

Following hard on the heels of the Comey firing Mueller had been appointed to conduct an investigation into Russian links to Trump's 2015- 2016 presidential campaign.

The following day, 16 March, U.S. ABC News reported:

Former FBI deputy director Andy McCabe was fired Friday from the federal government, just two days before he was set to retire, Attorney General Jeff Sessions announced in a statement late Friday night.

Nearly 24 hours earlier, McCabe was inside the Justice Department making the case to keep his job until Sunday when he officially qualifies for retirement benefits. His firing means his full pension — built after nearly 22 years in government — is in jeopardy.

After formal announcement of the McCabe sacking Trump tweeted this:

That Trump's move against McCabe is a step on the road to firing Special Counsel Robert Mueller might be inferred from the Dowd quote below. 

According to The Daily Beast  on 17 March 2018:

“I pray that Acting Attorney General Rosenstein will follow the brilliant and courageous example of the FBI Office of Professional Responsibility and Attorney General Jeff Sessions and bring an end to alleged Russia Collusion investigation manufactured by McCabe’s boss James Comey based upon a fraudulent and corrupt Dossier,” Dowd then wrote.

He told The Daily Beast he was speaking on behalf of the president, in his capacity as the president’s attorney.

McCabe's response.....

Statement released by Andrew McCabe's lawyer - sourced from Twitter