WASHINGTON — A simmering conflict between the White House and congressional Democrats intensified this week after the Pentagon confirmed it is reviewing whether Senator Mark Kelly, a former Navy pilot and NASA astronaut, may have violated military law by participating in a video reminding U.S. service members that they are not obligated to follow unlawful orders. The move, which followed public criticism from former President Donald J. Trump and conservative commentator Pete Hegseth, has raised concerns among legal scholars, military ethicists, and lawmakers about the politicization of the armed forces.

The controversy began when Kelly appeared in a short video alongside several other Democratic lawmakers reiterating the long-established principle that military personnel may refuse illegal directives. The message referenced recent judicial rulings and previous episodes in which Mr. Trump, during his first term, sought the deployment of federal troops to U.S. cities and reportedly asked advisers about using force against protesters.

In the video, Kelly told active-duty service members: “You all swore an oath… Our laws are clear. You can refuse illegal orders. Your vigilance is critical.”

The video circulated widely last week but drew renewed attention after Mr. Trump called the participating lawmakers “seditious” on his social media platform and said they should face severe punishment. According to aides, Kelly was informed of the former president’s comments by staff during a committee meeting. “She comes back later and she says, ‘Oh, yeah, he also threatened to have you executed,’” Kelly recounted in an interview.

On Monday, the Department of Defense issued a statement saying it was examining “serious allegations of misconduct” related to the video. The review specifically concerns Kelly because he is a retired naval commander and therefore still subject to certain provisions of the Uniform Code of Military Justice (U.C.M.J.). Other lawmakers in the video, whose military service ended under different categories, would not fall under the same regulations.

The Pentagon cited U.C.M.J. provisions prohibiting actions that interfere with the “loyalty, morale, good order, and discipline” of the armed forces. Officials did not say whether a formal investigation had been opened nor whether a court-martial was likely — a step legal experts say would be extremely rare.

A Pentagon spokesperson declined to elaborate beyond the initial statement.

Kelly has not yet issued a detailed response but said over the weekend that he “won’t be intimidated from doing [his] job.” His office did not comment further on Monday.

The episode immediately spilled onto Capitol Hill, where Republican allies of Mr. Trump echoed the former president’s accusations of sedition while Democrats denounced the Pentagon’s move as an overreach. Several senior Democratic aides said they were “surprised” by the speed with which the Department of Defense responded and questioned whether political pressure from Mr. Trump or his allies had influenced the Pentagon’s posture.

Mr. Hegseth, a former Army officer and current Fox News host, amplified the former president’s remarks, arguing that Kelly’s participation in the video could undermine military discipline. Legal analysts, however, noted that Kelly’s statements closely mirrored longstanding Pentagon guidance and federal case law affirming that unlawful orders need not be followed.

“There is nothing novel about reminding troops of their obligations under the Constitution,” said Rachel VanLandingham, a former Air Force judge advocate and professor of military law. “The concern here is less about the content of the message and more about the possibility that routine civic expression is being reframed as misconduct.”

Several former military leaders warned that framing the issue as sedition risked dragging the armed forces into political conflict. “Even the suggestion of a court-martial for a sitting senator, based solely on his public speech, is unprecedented,” said retired Rear Adm. Gene Price. “It sends a chilling signal about how military authority might be leveraged in future political disputes.”

The Pentagon’s statement also comes as Mr. Trump has increasingly criticized military leaders and pledged to assert greater personal control over the armed forces if he returns to office. His prior suggestions — including firing senior officers who resist his directives and expanding presidential authority over troop deployments — have already prompted debate about the limits of civilian oversight.

For now, it remains unclear how far the Pentagon review will go. Officials familiar with the process said any move toward formal discipline for Kelly would face significant legal hurdles and would almost certainly trigger a constitutional fight over the separation of powers.

But even without further action, the episode underscores mounting tensions surrounding military independence and the role of retired officers in public life. As political rhetoric intensifies, analysts say the Kelly-Hegseth clash may foreshadow broader battles over the boundaries of lawful authority — and the willingness of institutions to resist pressure from political leaders.

“This is not just about one video,” said Kori Schake, a defense policy expert at the American Enterprise Institute. “It’s about whether the military becomes a political weapon. That question will shape American democracy far beyond this moment.”