CHICAGO >> Texas church shooting victims and their families could have a hard time successfully suing the government over the Air Force’s failure to submit the gunman’s criminal history to the FBI — a step that would have blocked him from legally buying weapons.

Relatives of the more than two dozen churchgoers killed in Sunday’s attack would face major obstacles, including protections written into law to shield the military from certain legal action. An easier route might be to seek help from Congress, which could pass a law acknowledging the Air Force’s mistake and offering compensation.

A look at some of the key issues involved:

WHO TO SUE

There are just two plausible targets for a lawsuit, legal experts say: Kelley’s estate and the Air Force. Suing for Kelley’s assets would be an easy legal win. But it is likely to result in payments of no more than a few hundred dollars to each of the families whose loved ones were killed or wounded.

Targeting the Air Force means taking on the U.S. government. The United States, not the Air Force, would be named in any lawsuit as the defendant. Lawyers from the Department of Justice would represent the government.

At issue would be Devin Patrick Kelly’s purchase of the Ruger AR-15 used in the attack. The Air Force did not report his 2012 court-martial for abusing his wife and her child to a federal database used for background checks on gun purchasers. Had that conviction been entered into the database, as required by Pentagon rules, Kelley’s legal purchase of any gun would have been denied.

Kelley, who worked in logistics at the Holloman Air Force Base in New Mexico starting in 2010, was given 12 months of confinement followed by a bad-conduct discharge in 2014.

CAUSE AND EFFECT

The question at the core of any civil case would be: Did the clerical failure by the Air Force cause the deaths in Texas?

Proving such a direct link wouldn’t be easy, said Tony Romanucci, a leading personal injury attorney based in Chicago.

“In a regular negligence case, you only have to prove some act was ‘a’ cause of an injury,” he explained. But according to federal statutes that lay out the ground rules for suing the government, “you have to show it is ‘the’ cause of the injury. … That is a much, much higher standard.”

Government attorneys would have to concede the Air Force error made it easier for Kelley to buy guns. But they would almost certainly argue in court that, by any meaningful definition of cause and effect, Kelley caused the deaths and bears sole responsibility for the killings.

LAWS AT PLAY

The 1946 Federal Tort Claims Act opened the way for Americans to sue the government. But it and other statutes also leave an important role to laws of the states where the negligence allegedly occurred. A lawsuit filed in federal court in Texas against the U.S., for instance, would use the legal criteria for negligence adopted by Texas.

Federal laws do provide partial shields from legal action to the U.S. government, including the military. For instance, plaintiffs cannot sue the government on the basis that a government policy caused injuries. They must show that a specific wrongful act or negligence by an agency or by a government employee caused the injury — not that the overall policy did.

Federal employees cannot be sued individually. And the military cannot be sued for strategic decisions or commands that lead to soldiers’ deaths.

CHANCES OF SUCCESS

If a lawsuit is filed, the government could choose to seek a settlement before the case gets to trial. But federal authorities have typically dug in to fight litigation for fear that giving in too easily would invite a flood of similar litigation.

One risk of going to trial would be that sympathetic jurors end up awarding plaintiffs far more in damages than they might have been willing to settle for earlier.

“You can’t think of a more sympathetic group of individuals — children and worshippers on a Sunday gunned down,” Romanucci said. “What they will get … you are looking at (a potential award of) tens and ten of millions of dollars.”

CONGRESSIONAL OPTION

Given the complexities involved in suing a governmental body, it is possible, perhaps even likely, that U.S. district and appellate courts will rule that the Air Force is not liable and dismiss any lawsuits outright, explained Gregory Sisk, a professor at the University of St. Thomas School of Law in Minneapolis.

But, he added, that does not mean compensation by the government is out of the question.

It is within the powers of Congress to pass a new law tailored specifically to the Texas shooting, one that could acknowledge the Air Force’s mistake and offer a compensation package.

Though relatively rare, Sisk said, moving the matter from the courts to Congress is an option lawmakers have taken in cases when there’s public sympathy for victims of some government action or inaction, such as people who claimed U.S. nuclear tests decades ago made them ill.