"Obstruction of justice is an intent crime. If his intent was to impede, interfere or stop that investigation, that's obstruction," Ackerman said.

He recalled that the president said, "I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go."

"The Comey testimony today makes that crystal clear," Ackerman said in an interview with " Closing Bell ."

There's "no question" President Donald Trump was involved in an obstruction of justice in his dealings with former FBI Director James Comey, former assistant special Watergate prosecutor Nick Ackerman told CNBC on Thursday.

What's more, he thinks there was a motive. He said he doesn't believe "for a minute" that Flynn had dealings with Russia on his own, without Trump knowing about it.

"The bottom line is the president is worried that Mike Flynn is going to turn into the next James McCord, the Watergate burglar who wound up getting a heavy sentence and then fingering the people in the White House," Ackerman said.

He believes it all adds up to "one big obstruction of justice."

Trump's personal lawyer, Marc Kasowitz, didn't immediately respond to a request for comment but released a statement earlier Thursday afternoon after Comey's testimony.

Kasowitz said Comey was lying and that Trump never "directed or suggested that Mr. Comey stop investigating anyone."

Robert Ray, former independent counsel for the Whitewater investigation, believes the notion that Trump's actions amount to criminal obstruction of justice is "far-fetched."

"Whatever the president's hopes and intimations were, he didn't issue a directive or an order to the FBI director to end any investigation," Ray told "Closing Bell."

And even if it were true that the president actually ordered the FBI director to halt an investigation, it still isn't obstruction of justice, he added.

"The president is entitled to do that. You may not like it. The Congress might decide that is grounds for an impeachable offense, but it is not criminal obstruction of justice," said Ray.

To Ackerman he said, "Good luck trying to prove that corrupt intent."

—CNBC's Jacob Pramuk contributed to this report.