WASHINGTON (AP) — The Pentagon’s probe into Senator Mark Kelly regarding a video encouraging American troops to disobey “illegal orders” has sparked a mix of questions and criticisms from legal experts.

Some experts argue that the Pentagon is misinterpreting military law in its pursuit of Kelly, who is a retired Navy fighter pilot. Others contend that the Arizona Democrat is immune from prosecution in his capacity as a member of Congress. Meanwhile, a group of former military prosecutors is staunchly defending him, asserting that he has done nothing wrong.

The Pentagon announced the investigation following a social media post by President Donald Trump, accusing Kelly and five other Democratic lawmakers featured in the video of sedition, which he claimed is “punishable by DEATH.”

Defense Secretary Pete Hegseth explained that Kelly is under scrutiny because he is the only individual in the video who has retired from the military and thus remains within the Pentagon’s jurisdiction.

In response, Kelly has brushed off the inquiry, labeling it as an effort by “bullies” and affirming that it will not deter him or his fellow Congress members from “doing our jobs and holding this administration accountable.”

‘It’s not totally unheard of’

Stephen Vladeck, a Georgetown University law professor, said there has been a “significant uptick” in courts-martial of retired service members in the past decade. While courts have debated the constitutionality, the practice is currently allowed. He said there have been roughly a dozen such prosecutions across the service branches.

There are roughly 2 million people who formally retired from the military and receive retirement pay, according to a report from the Congressional Research Service. Service members are generally entitled to retirement pay after completing 20 years of active duty.

Todd Huntley, a retired Navy captain and judge advocate general, or JAG, said it is rare to prosecute retirees for something that happened after they retired.

“It’s not totally unheard of,” said Huntley, who now directs Georgetown’s national security law program. “I actually prosecuted a enlisted guy who had been retired for 16 years. He was essentially assaulting his adopted daughter. Basically no one else had jurisdiction so we prosecuted him.”

A ‘ridiculous conclusion’

Colby Vokey, a prominent civilian military lawyer and former military prosecutor, said Hegseth appears to be misreading the Uniform Code of Military Justice to justify the Kelly investigation.

Vokey said Hegseth has personal jurisdiction over Kelly because Kelly is entitled to retirement pay. But Vokey said Hegseth lacks subject matter jurisdiction because Kelly made his statements as a senator.

Vokey said case law has evolved to where the military can prosecute an active-duty service member for a crime committed off base, such as robbing a convenience store. But applying military law to a retired service member and “assuming that means every offense ever is kind of a ridiculous conclusion.”

“Let’s say you have a 100-year-old World War II veteran who is retired with pay and he steals a candy bar,” Vokey said. “Hegseth could bring him back and court-martial him. And that in effect is what is happening with Kelly.”

Patrick McLain, a retired Marine Corps judge and former federal prosecutor, said the cases he has seen of retirees being called back “are more like extreme examples of fraud or some of these child pornography cases.”

“I’ve not seen anything like the kind of the wackadoodle thing they’re trying to do to Sen. Kelly for essentially exercising his First Amendment right to free speech, which they don’t like,” McLain said.

‘He did it as a civilian’

Charles Dunlap, a Duke University law professor and retired Air Force lawyer, said in an email that military law can restrict speech for service members that is protected for civilians under the First Amendment.

But even if the video was found to have violated military law, a key issue may be whether the law can be applied to someone who is retired, Dunlap said.

A group of former military lawyers, the Former JAGs Working Group, said in a statement that Kelly did not violate the Uniform Code of Military Justice.

“The video simply described the law as it pertains to lawful versus unlawful orders,” the group said. “It did not suborn mutiny or otherwise encourage military members to disregard or disobey lawful orders issued to them.”

Troops, especially uniformed commanders, have specific obligations to reject orders that are unlawful. Broad legal precedence also holds that just following orders — colloquially known as the “Nuremberg defense,” as it was used unsuccessfully by senior Nazi officials to justify their actions under Adolf Hitler — does not absolve troops.

Kelly and the other lawmakers did not mention specific circumstances in the video. Some Democratic lawmakers have questioned the legality of the Trump administration’s attempts to send National Guard troops into U.S. cities. Kelly has pointedly questioned the use of the military to attack alleged drug boats off South America’s coast, saying he was worried about the military officers involved with the mission and whether they were following orders that may have been illegal.

Michael O’Hanlon, director of research in the foreign policy program at the Brookings Institution, said any case brought against Kelly likely would be thrown out or end in an acquittal.

O’Hanlon said it might not have been politically smart to “wave a red flag in front of the bull” but he does not see the legal grounds for a court martial.

“Saying that you shouldn’t break the law cannot be a crime,” O’Hanlon said. “But in addition, he did not do it as a military officer. He did it as a civilian.”

Separation of powers

Kelly’s status as a senator could block the Pentagon’s investigation because of constitutional protections for the separation of powers in the U.S government.

The Constitution explicitly shields members of Congress from White House overreach, said Anthony Michael Kreis, a constitutional law professor at Georgia State University.

“Having a United States senator subject to discipline at the behest of the secretary of defense and the president — that violates a core principle of legislative independence,” Kreis said in a telephone interview.

Kreis said such protections were a reaction to the British monarchy, which arbitrarily punished members of Parliament.

”Any way you cut it, the Constitution is fundamentally structurally designed to prevent this kind of abuse,” Kreis said.