Peter Navarro, a former senior aide to President Donald Trump, turned himself in to a Miami jail Tuesday, a day after the Supreme Court declined to delay his prison time while he appeals his conviction for refusing to testify before Congress about his involvement in efforts to overturn the 2020 presidential election.

Speaking to reporters before reporting to a federal prison around 11:30 a.m. Tuesday, the 74-year-old economist claimed that, by incarcerating him, the justice system was dealing a “crippling blow to the constitutional separation of powers and executive privilege.”

Navarro insisted that he was protected from testifying before Congress by executive privilege, an oft-cited but loosely defined legal protection designed to give the president and top White House aides confidentiality as they make tough decisions while governing, without fearing that those private conversations will be publicly scrutinized.

Before entering the jail, Navarro insisted he had done nothing wrong by ignoring a congressional subpoena and said his ultimate goal was to “defend the Constitution,” the separation of powers, and executive privilege.

“I knew, from Day One and getting that subpoena, based on my experiences in the White House, reading the Office of Legal Counsel memos at the Department of Justice, that absolute testimonial immunity was in place,” he said. Navarro then listed a number of other top Trump administration aides — including adviser Kellyanne Conway, counsel Donald McGahn and deputy chief of staff Rick Dearborn — who “did exactly what I did, and were never prosecuted.”

But — unlike those witnesses in investigations into the Jan. 6, 2021, attack on the U.S. Capitol and Russian interference — Navarro had no documentation to show that Trump ever planned to assert that privilege to keep his aide from testifying, and Trump has never publicly corroborated Navarro’s account.

“If I had gone to Congress, and played the piecemeal game with them, I would have done damage to the separation of powers and I would not have been doing my duty,” Navarro said. Prosecutors have said that even when executive privilege applies, a witness is required to respond to a subpoena and explain what specific testimony or documents they believe are off-limits.

After the attack on the Capitol, Navarro published a book in which he described a plot to throw the election to Trump during the counting of electoral votes that day. He credited the idea to right-wing podcast host and former Trump strategist Stephen K. Bannon.

When the special House committee tasked with investigating the attack issued subpoenas for Navarro and Bannon to elaborate on those plans, both men ignored them. Now the two are fighting prison sentences for contempt of Congress. The district court judge presiding over Bannon’s case, however, allowed him to stay out of prison while Bannon pursued an argument on appeal not available to Navarro — that in refusing to testify, he was relying on advice from his attorney.

Navarro’s attorneys, who declined to comment Monday after Chief Justice John G. Roberts Jr. issued his decision, have argued that Navarro refused to comply with a congressional subpoena because he thought he was required to assert executive privilege. They argued that the law is not clear on whether Congress intended to punish senior presidential advisers in such circumstances.

Navarro was sentenced in January to four months after a jury convicted him on two counts of contempt of Congress. Last week, the U.S. Court of Appeals for the D.C. Circuit refused Navarro’s request to remain free. A three-judge panel said Navarro “has not shown that his appeal presents substantial questions of law or fact likely” to undo his conviction or sentence.

And, on Monday, Roberts — who oversees emergency requests from the D.C. Circuit — said he saw no basis to disagree with the court ruling.

That meant Navarro had to turn himself in to jail by 2 p.m. on Tuesday.

Before entering the facility, Navarro continued to claim that he was protected from testifying before the Jan. 6 committee because he was a close White House adviser to Trump.

“I am the first senior White House adviser in the history of our republic that has ever been charged with this alleged crime,” Navarro said.

“For 50 years, the Department of Justice has maintained the principle of absolute testimony immunity, and it was only with my case that somehow that has changed,” he said.

Navarro argued that Congress could not compel him to testify because, as a senior White House aide, he was an “alter ego of a president” and thus is protected by executive privilege — which, as first established by President George Washington in 1796 during negotiations for the Jay Treaty, protects close White House advisers from discussing conversations with the president.

Washington, however, advocated for a limited use of executive privilege, arguing that he was only invoking it during the Jay Treaty negotiations to protect national security and the country’s ability to negotiate international treaties in the future.

Speaking outside the jail, Navarro remained steadfast in his support of Trump, attacked President Biden’s policies and urged others to vote for Trump in the November election.

“I am not nervous,” Navarro said about going to jail. “I had the greatest amount of support from Donald Trump and his team.”

Navarro — clad in a black T-shirt and a gray jacket — also complained at length about the Justice Department. He repeated baseless conspiracy theories that the Jan. 6 attack was instigated by undercover FBI agents and Democrats.

Navarro then accused the Justice Department of “coming after Donald Trump with the same tactics, tools and strategies they used to put me over there today,” citing the multiple investigations Trump is facing. The former president and his allies repeatedly claim, baselessly, that the Justice Department has been weaponized against them.

“I’m pissed,” Navarro said, adding that he’s “afraid for this country because this, what they’re doing, should have a chilling effect on every American regardless of their party. They come for me; they can come for you.”

Navarro promised that, once his sentence was done, he would once again bring his case to the Supreme Court.

Ann E. Marimow contributed to this report.