WASHINGTON (Reuters) - U.S. President Donald Trump’s lead lawyer in the special counsel investigation into Russia’s role in the 2016 presidential election, John Dowd, resigned on Thursday, the same week Trump added another Washington lawyer to his team.

Dowd, a tough-talking ex-Marine, joined Trump’s legal team last June and took the lead during the summer after Marc Kasowitz, a longtime personal lawyer for Trump, stepped down. “I fight hard,” Dowd said in an interview at the time.

“I am not a snowflake,” he said, a disparaging term that has been used to mock liberals.

Since then the president has become increasingly frustrated that special counsel Robert Mueller’s probe has not gone away, said a person close to Trump who asked not to be named to discuss the matter.

“I love the president and wish him well,” Dowd, 77, told Reuters in an email on Thursday. In a telephone interview later, he declined to explain why he resigned.

Joseph diGenova, who was named to Trump’s legal team on Monday, has been a vocal proponent on right-wing media of what he calls a “brazen plot” by senior Justice Department and Federal Bureau of Investigation officials to clear Hillary Clinton of alleged criminal conduct for storing classified materials on her private email server when she was secretary of state.

According to diGenova, when Clinton lost the 2016 election to Trump, the officials, including former FBI Director James Comey, sought to ruin Trump with an investigation into possible collusion between his 2016 campaign and Russia.

Attorney Jay Sekulow, who also represents Trump, said on Monday diGenova was to join the team this week.

Dowd’s resignation was reported earlier on Thursday by The New York Times, which cited a source who said Trump was increasingly ignoring Dowd’s advice.

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Sekulow and Dowd had been negotiating a possible interview between Trump and Mueller, people familiar with the matter have said.

Sources have said the firings of Comey and former national security advisor Michael Flynn were among topics of interest to Mueller’s team in respect to Trump.

Mueller could issue a subpoena for Trump to appear before a grand jury if an interview cannot be arranged.

Trump has said that he looks forward to being interviewed by Mueller. On Thursday, when asked at an unrelated press briefing if he still wanted to testify before Mueller, Trump said, “Yes, I would like to.”

In a statement, Sekulow called Dowd “a friend” and “a valuable member of our legal team,” and he pledged continued cooperation with Mueller.

Last Saturday, Dowd called for an end to Mueller’s probe, which he said had been manufactured by Comey. The Daily Beast reported that Dowd said he was speaking for Trump, but he later rowed back on that and said he was speaking for himself.

Asked whether Trump had urged him to make the comment, Dowd later told Reuters, “He liked it, that’s all I’ll say.”

The addition of diGenova to the legal team might signal a more aggressive strategy by Trump to discredit Mueller.

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Mueller is investigating possible collusion between the Trump campaign and Russia to influence the 2016 presidential election. Trump has denounced the investigation as a “witch hunt.”

White House lawyer Ty Cobb, hired last summer to assist Trump with Mueller’s investigation, now also appears to be on shakier ground given his strategy, which has included cooperating with Mueller.

In an August interview with Reuters, Cobb predicted a quick end to the Mueller probe and said he would be embarrassed if the investigation was haunting the White House in 2018.

On Sunday, Cobb said that Trump was not considering or discussing firing Mueller. Cobb did not immediately respond on Thursday to requests to comment.

Earlier in March, veteran Washington lawyer Emmet Flood met with Trump for a possible White House job to help with the Russia probe. Flood advised former President Bill Clinton in impeachment proceedings.