President Trump on Monday. (Jabin Botsford/The Washington Post)

President Trump on Wednesday called an investigation of possible obstruction of justice a “setup & trap” in a defiant morning tweet in which he once again asserted that there was no wrongdoing to be uncovered in the special counsel inquiry.

Trump’s tweet comes amid ongoing negotiations between his lawyers and special counsel Robert S. Mueller III over whether the president will consent to an interview as part of the investigation of Russian interference in the 2016 presidential campaign.

In March, Mueller warned during a meeting with Trump’s lawyers that he could issue a subpoena for the president to appear before a grand jury, according to four people familiar with the encounter.

Mueller has been investigating whether Trump’s campaign colluded with Russia and whether the president has sought to obstruct the investigation, and he has signaled that he would like to question Trump in both areas.

“There was no Collusion (it is a Hoax) and there is no Obstruction of Justice (that is a setup & trap),” Trump wrote on Twitter on Wednesday morning, again calling the investigation a “Witch Hunt!”

He also suggested that he was more focused on the duties of his office, including negotiations about the denuclearization of North Korea and trade agreements.

Trump had said previously that he would be willing to have a face-to-face meeting with Mueller or his team, but more recently he has wavered on the prospect. Some of Trump’s advisers have counseled that he could risk being accused of perjury if he submits to open-ended questioning from Mueller and provides meandering answers.

Following a testy meeting in March, Mueller’s team agreed to provide Trump’s lawyers with more specific information about the subjects that prosecutors wished to discuss with the president.

With those details in hand, Trump attorney Jay Sekulow compiled a list of 49 questions that the team thought the president would be asked, according to people familiar with the encounter.

The questions focus on events during the Trump campaign, transition and presidency that have long been known to be under scrutiny, including the president’s reasons for firing then-FBI Director James B. Comey and the pressure he put on Attorney General Jeff Sessions to resign.

Earlier this week, Trump suggested on Twitter that he would not be vulnerable to obstruction charges if there were no coordination between his campaign and Russia.

“It would seem very hard to obstruct justice for a crime that never happened! Witch Hunt!” he wrote.

But that, many legal experts say, is a misunderstanding of the law, that people can be charged by prosecutors with obstruction of justice even if no underlying crime is proven.

Appearing on Fox News Channel on Wednesday, lawyer Victoria Toensing warned that Trump could be accused of perjury if something he said in an interview with Mueller conflicted with claims by Comey.

Toensing, who was recruited for Trump’s legal team but did not join because of client conflicts, recalled the case of I. Lewis “Scooter” Libby, the former chief of staff to Vice President Richard B. Cheney.

Libby, whom Toensing represented, was convicted of obstruction of justice and other charges in 2007 stemming from an investigation of a leak of a CIA officer’s identity. But Libby was never charged with leaking the officer’s identity.

Trump issued a pardon to Libby last month.

In two tweets later Wednesday morning, Trump quoted a sympathetic radio interview with Toensing’s husband, lawyer Joseph diGenova, and recommended a new book by Fox News legal analyst Gregg Jarrett called “The Russia Hoax: The Illicit Scheme to Clear Hillary Clinton and Frame Donald Trump.”

Trump quoted diGenova as saying that some questions Mueller wants to ask are an intrusion into the president’s constitutional power to fire executive branch employees.

Appearing on SiriusXM’s POTUS channel with Michael Smerconish on Monday, diGenova said Mueller is leading “an outrageous, sophomoric, juvenile intrusion into the president’s unfettered power to fire anyone in the executive branch.”

In his other tweet, Trump called Jarrett “brilliant” and said his book, which criticizes the FBI, is “A MUST READ.”

“A sad chapter for law enforcement,” Trump wrote. “A rigged system!”

Carol D. Leonnig and Robert Costa contributed to this report.