Jim Comey gave Congress more than enough grounds to impeach President Donald Trump on a charge of obstruction of justice, according to a top criminal defense lawyer who said the former FBI director's account of being pressured by the president to drop a probe is highly believable.

"I think he's probably the most credible witnesses that's ever appeared before that committee or any other congressional committee," said Gerald Lefcourt, a New York attorney, after Comey finished his testimony to the Senate Intelligence Committee on Thursday.

"I can't think of anybody thought of as more credible," said Lefcourt, who defended people criminally charged by Comey when the former FBI director was the top federal prosecutor in Manhattan. "This is one of the straightest arrows you've ever seen."

Comey testified that Trump leaned on him to drop an investigation into the president's former national security advisor, Michael Flynn, regarding his contacts with Russians. Comey also said he told other people about this pressure from Trump, and detailed his contacts with the president in memos written right after speaking with him.

Lefcourt said Comey's claims, combined with his memos and accounts to others, as well as Trump's own public words and tweets about Comey and the probe, means "there's more enough probable cause" to warrant Trump being charged with obstruction of justice.

"That's enough evidence to put it before a jury," Lefcourt said.

However, the Justice Department has a policy that bars sitting presidents from being criminally charged by that agency.

That would mean that Trump's vulnerability is with Congress, which has the power to impeach him, and try him in the Senate for high crimes or misdemeanors, if members of Congress see fit.

Lefcourt said, "I believe he [Comey] thinks" Trump should be impeached.

John Carlin, a former assistant attorney general for the Justice Department's national security division, said that "what we have here is testimony that the president of the United States had a private meeting with the director of the FBI ... [and] he pressured him to drop the investigation of Michael Flynn."

"That could rise to the level of an impeachable offense, and that will be up to the members of Congress to determine," Carlin said on CNBC's "Power Lunch."

Comey himself testified Thursday that "I took it as a very disturbing thing, very concerning," when asked if he believes Trump's pressure on him qualified as obstruction of justice.

However, he added, "But that is a conclusion I am sure the special counsel will work towards to try and understand what the intention was there and whether that was an offense."

Robert Mueller, a former FBI director, has been appointed special counsel in the probe of Russian influence in the presidential election.

Chris Swecker a former FBI assistant director who also appeared on "Power Lunch," noted "Mueller is looking into this issue, so, yes, it's going to lead to a potential obstruction of justice charge or an investigation."

Swecker said the obstruction of justice law is "a very difficult statue to work with" for prosecutors.

One major question is whether investigators would be able to prove that Trump intended to interfere with Comey's probe into Flynn, or whether he was just suggesting that Flynn deserved a break.

Watch: Entire Comey testimony