President Trump should be more than a little worried about the plea deal his former lawyer Michael Cohen made with special counsel Robert Mueller.

Senior legal figures told the Washington Examiner that the plea deal could be damning for the president, based on their lengthy and intricate relationship.

[READ: Michael Cohen's plea agreement]

Joseph Moreno, a former federal prosecutor, said that when Cohen was raided by the FBI in April, "many believed that his knowledge of President Trump’s business dealings would be the greatest threat to this administration."

That theory died down in the recent months, explained Moreno, but it "re-emerged in full force this week" following Cohen's plea deal.

"The idea that Cohen is not a bit player simply facing tax charges in New York, but in fact appears to have provided significant information to special counsel Mueller, is a significant development in the Russia probe and could potentially spell significant trouble for President Trump both legally and politically," Moreno told the Washington Examiner.

Another former federal prosecutor described Cohen, among all of the potential cooperating witnesses in Mueller's inquiry, as "the one true wild card."

"[G]iven Cohen’s longstanding relationship with President Trump and the Trump Organization, Cohen’s decision to enter a guilty plea and to cooperate with the Mueller investigation raises the stakes for the president’s defense team since it may be difficult for them to learn exactly what Cohen knows and what assistance he could provide to the special counsel," explained Robert Mintz, who is now head of the white collar criminal defense practice at the law firm McCarter & English, to the Washington Examiner.

"At a minimum, how close Mr. Cohen has been to the president means that the special counsel will have insights and information at a level that breaks new ground for the investigation," Jacob S. Frenkel, a former federal prosecutor and Securities and Exchange Commission enforcement lawyer, told the Washington Examiner. "The quality, reliability and substance of the information alone will determine how problematic the information may be for the president."

Since his appointment in May 2017, Mueller has secured a string of guilty pleas from former advisers and associates of Trump.

None of them dealt directly with connections between the Russian government and the inner circle of Trump until Cohen's plea deal.

Cohen, 52, worked as Trump's lawyer, and once said he would take a bullet for Trump. He pleaded guilty Thursday in federal court in New York to lying to Congress about a Trump Tower project in Moscow he pursued during the 2016 presidential election.

In August, Cohen pleaded guilty to campaign finance violations and financial crimes in a case brought by the U.S. attorney in Manhattan. In his plea deal, Cohen implicated the president in the hush-money payment scheme to keep two women quiet about their alleged affairs with Trump during the 2016 presidential election.

Late Friday, lawyers for Cohen, Guy Petrillo and Amy Lester, filed a memo in which they asked a federal judge that their client avoid prison time when he is sentenced for both cases in which he pleaded guilty on Dec. 12.

Cohen could have fought the charges brought by the federal government, thus "positioning himself perhaps for a pardon or clemency,” the lawyers said.

“Michael regrets that his vigor in promoting Client-1’s [Trump's] interests in the heat of political battle led him to abandon good judgment and cross legal lines,” his lawyers wrote, saying Cohen acted out of his “fierce loyalty” to the president.

In the months since the August plea deal, and the hours following this week's plea deal, Trump has sought to distance himself from his former self-described "fixer."

"He's a liar," Trump said as he left the White House Thursday for Argentina. "He's a weak person and what he's trying to do is get a reduced sentence."