A Kuwait-based Army captain has been doing fine at work since he filed a lawsuit this week challenging the legality of the U.S. military campaign against the Islamic State group, one of his attorneys says.

Among Capt. Nathan Michael Smith's colleagues there's been no open disapproval of what could become a landmark legal action or a trigger for congressional action, his attorney David Remes says.

"He has divided the reactions into three categories: overtly supportive, discreetly supportive and the third group is an x-factor, they don't say one way or the other," Remes says, attributing the observation to a Friday phone call with his client after a day of intense media coverage Thursday.

"He's not been getting dirty looks, I can guarantee you of that," Remes says. "He's not in the brig and he hasn't been transferred, so I told him 'Just keep doing your job' and that's what he's going to do."

Smith, 28, joined the military in 2010 after graduating from the University of San Diego and says in the lawsuit he supports fighting the fanatical religious group that rules wide swaths of Syria and Iraq, but believes President Barack Obama currently has no legal authority to order the operation.

Obama says a 2001 anti-al-Qaida congressional resolution authorizing military force against entities that "planned, authorized, committed, or aided" the 9/11 attacks authorizes an open-ended military campaign against the jihadi group in Iraq and Syria, but skeptics point out the group since 2014 has fought against al-Qaida's affiliate in Syria.

Smith and many legal scholars disagree with Obama's claimed power to fight the group also known as ISIS or ISIL. The Obama administration says a 2002 war authorization passed before the invasion to topple Iraq's Saddam Hussein provides overlapping authority for Iraq operations.

The Constitution grants Congress the power to declare war, and the War Powers Resolution – enacted in response to secret expansion of the Vietnam War – limits use of force abroad to 60 days without congressional authorization, with an extra 30 days allowed for disengagement. The war against ISIS has gone 21 months without specific legislative authorization, but with incremental increases in troop deployments.

The lawsuit is the brainchild of Yale Law School professor Bruce Ackerman, who last year floated a theory that an active-duty member of the military who's ordered to participate in the war effort would have standing to sue in court.

Standing typically kneecaps challenges to the legality of wars that lack specific congressional authorization, resulting for example in the dismissal of a lawsuit brought by 10 congressmen against Obama's 2011 intervention in Libya.

But Ackerman theorizes the soldier would meet the Constitution's standing requirement of a "concrete and particularized" injury fairly traceable to the challenged action and redressable by a favorable ruling. He believes after meeting that burden, soldier can prevail on the merits of the claim. Smith alleges his injury is the forced violation of a pledge to defend the Constitution.

Ackerman's view hasn't met universal acclaim. When he shared the theory with U.S. News in July, the National Institute of Military Justice's co-founder Eugene Fidell scoffed, "I wouldn't take that case on a contingency basis!" Fidell argued it would be dismissed as a non-justiciable political issue.

But Ackerman laid out a more detailed history of such claims, including two lawsuits from soldiers challenging the constitutionality of the Vietnam War that made it into court, in an August article in The Atlantic. And Smith ultimately read that article and contacted the professor earlier this year.

Other people had expressed interest. Ackerman in October, for example, told U.S. News he had found potential plaintiffs, well before Smith signed on to the effort.

"People called me and we talked a bit and they didn't follow up," he recalls. "It isn't as if these concerns aren't recognized as serious in the military. It isn't as if Capt. Smith is an exception, people recognize there is a problem."

Ackerman says he and Smith had in-depth discussions and that "he's a highly intelligent person, very thoughtful, and I hope there are lots more like him in the military."

Ackerman referred Smith to Remes, who currently represents 12 of 80 detainees at the Guantanamo Bay prison camp. He says he will remain a consultant on the case, but believes Remes, who retired early from a prestigious corporate law firm, is well-suited to lead the effort.

"I wanted someone who was a senior lawyer of proven ability, but I didn't want to make this into a hyper-partisan case," the professor says.

Though a bold action, military law experts say Smith appears unlikely to face any discipline within the military for filing the lawsuit.

"I can't think of any punishment under the [Uniform Code of Military Justice] that Captain Smith would get," says Richard Rosen, a former commandant of the U.S. Army Judge Advocate General's School who teaches at the Texas Tech University School of Law.

"I'm not sure the complaint reflects good judgment," he says. "Maybe he will be admonished or something, but I don't think the Army would retaliate against him."

Rosen says he's never heard of a soldier being punished for filing a federal lawsuit and says he doubts Smith's commander would attempt to stretch the offenses of conduct unbecoming of an officer or jeopardizing good order and discipline to justify discipline.

An adverse comment on officer evaluation report is the most he could foresee as discipline, says Rosen, who believes Smith's lawsuit will fail and that Congress' funding of the war constitutes an implicit endorsement. He's also not convinced Smith has standing.

"If I were a legal adviser, I would tell his commander to do nothing, unless he's voicing his concerns in public with his troops or things like that," he says.

Lisa Schenck, a former military attorney and judge who now is an associate dean at the George Washington University's law school, says she also doubts Smith would be in legal trouble for filing the lawsuit.

Schenck says Article 88 of the UCMJ criminalizes contemptuous and disrespectful criticism of the president or other U.S. officials, but that Smith's lawsuit appears not to violate that law.

Members of the military, she says, are free to complain to members of Congress and their superiors, but that they must do so respectfully, something it appears Smith has done in the lawsuit.

"There's no name-calling," she says after scanning the lawsuit. "He's not saying the president is a this-and-a-that and that he's not going to follow orders. … He's addressing the policy rather than the president."

Schenck says other recent cases provide examples of what it takes to attract criminal charges. Army Lt. Col. Terry Lakin was sentenced to prison in 2010 after refusing to deploy to Afghanistan, claiming Obama was not born in the U.S. and therefore wasn't able to be president. Sgt. Gary Stein, meanwhile, was given an "other than honorable" discharge from the Marines in 2012 for writing on Facebook, "Screw Obama. I will not follow all orders from him."

Schenck says there could be legal consequences if Smith encourages fellow soldiers to join his lawsuit or if he is accused of disobeying a lawful order, but that she believes he currently appears safe from punishment under the UCMJ.

"This guy is just calmly litigating a constitutional issue," she says, adding however that "it's probably not great for his military career."

Justice Department spokespeople declined to comment on the case, as did the Defense Department.

The Combined Joint Task Force – Operation Inherent Resolve, to which Smith is assigned, said in a statement he has not been disciplined or reassigned as a result of the lawsuit. "There is no change to Capt. Smith's status. He continues to serve in the CJTF-OIR headquarters," the statement says.

Obama last year proposed an Islamic State group-specific war authorization, but Congress has not acted to pass the legislation. It's possible the lawsuit will spur lawmakers to action.

Last year, Rep. Jim McGovern, D-Mass., one of the most vigorous critics of the current war lacking congressional authorization, told U.S. News, "if someone [sues] it clearly raises awareness and pressure on Congress" to act.

Remes says he received a call Thursday from a veteran saying many soldiers feel like Smith does, and that he may add other active-duty servicemembers to the case. The attorney says congressional action to close the open-ended 2001 authorization could be one positive outcome of the case.