Could Trump's "witch hunt" tweet come back to haunt him?

The tweet from President Trump on Friday was more of a squawk. He complained, "I am being investigated for firing the FBI director by the man who told me to fire the FBI director! Witch hunt."

The president's tweet appeared to confirm a Washington Post report that special counsel Robert Mueller is investigating him for obstruction of justice. And it lashed out at Deputy Attorney General Rod Rosenstein, who the president had praised just last month.

"He's highly respected, very good guy, very smart guy," Mr. Trump said in April about Rosenstein. 

Rosenstein had written a memo critical of James Comey's handling of the Hillary Clinton email server. The White House initially said that was the main reason for the FBI director's dismissal.

President Trump complained of a "witch hunt" in a tweet about firing FBI Director James Comey. CBS News

"This Russia thing with Trump and Russia is a made-up story," Mr. Trump said in April. 

But the president said the FBI's Russia investigation was a key factor and that he had been planning to fire Comey before hearing from Rosenstein.

"He made a recommendation -- but regardless of recommendation, I was going to fire Comey, knowing there was no good time to do it," Mr. Trump said in April. 

Trump tweets about probe 03:48

Rosenstein is a career federal prosecutor who took over the Russia investigation after Attorney General Jeff Sessions recused himself. When it was revealed that Comey had kept detailed memos on his interactions with the president, Rosenstein appointed Mueller as special counsel.

The president's defenders have also been attacking Mueller, who served presidents of both parties as FBI director. They say he too is part of what Mr. Trump calls a partisan witch hunt.

Now Rosenstein is under scrutiny. Constitutional law professor Jonathan Turley says Rosenstein should recuse himself because of his interactions with Mr. Trump. 

"I can't imagine the special counsel completing this investigation without hearing the testimony from the deputy attorney general," Turley said. "So once you think you may be a witness, it's time for you to remove yourself." 

Russia probe frustration 02:22

And Turley notes the president's tweet could come back to haunt him.

"Any statement the president makes in any form can be evidence that can be used in an obstruction prosectuion," Turley said. 

In fact, White House press secretary Sean Spicer said the president's tweets should be taken seriously.

"The president is the president of the United States, so they are considered official statements of the president of the United States," Spicer said.  

The Justice Department says Rosenstein has no plans to recuse himself. On Thursday night, he issued a statement echoing the president's sentiments about press coverage of the Russia investigation. It decried anonymous sources and urged Americans to be "skeptical about anonymous allegations."