The fight over government-funded research on gun violence is heating up after several mass shootings during President Trump's first year in office.

Some Democratic lawmakers are pressuring the Trump administration to send a clear message that it will fund gun violence research, while others say it's time to rewrite the Dickey Amendment, a 1990s-era law banning tax dollars from going toward advocating or promoting gun control.

But without a majority in Congress or lack of support from the administration, they may run up against a wall. The National Rifle Association opposes the changes, saying the law is defined narrowly enough, while Republicans have been largely silent on research possibilities, focusing instead on legislation that would keep guns from ending up in the wrong hands.

One vehicle Democratic lawmakers have targeted is a National Institutes of Health call for research projects on gun violence that expired as planned on Jan. 8, 2017, shortly before Trump was inaugurated. It was issued in 2013, when former President Barack Obama told health agencies to fund or carry out research "into the causes of gun violence and the ways to prevent it," following the mass shooting at Sandy Hook Elementary School in Newtown, Conn.

Democratic senators, including Elizabeth Warren of Massachusetts, Chris Murphy of Connecticut, and Catherine Cortez Masto of Nevada, sent an October letter urging the NIH to "renew the gun violence research program as soon as possible." Democratic House members sent their own letter in November, inquiring about whether the funding had been discontinued and why, but they haven't heard back.

NIH officials told the Washington Examiner that it was not accurate to characterize funding for research on gun violence as having ended. It noted it had other ways to show it was interested in funding such grants, including through research priorities posted on its website. The call for research, formally known as a "program announcement," was just one way to communicate its intentions, it said.

"Program announcements are not programs. They are announcements to draw attention to a particular programmatic area of research and typically do not have funds dedicated to them," the NIH said. "The expiration of a program announcement doesn’t mean that the program supporting the announcement has ended or that funding is no longer available."

The nearly $19 million in grants were issued under the title "Research on the health determinants and consequences of violence and its prevention, particularly firearm violence." Twenty-three projects, some over several years, were funded from 2014 to 2017. Not all explicitly studied gun violence, however. One grant, for instance, went toward research that examined how intoxication affected a bystander's likelihood to intervene in a rape. In all, 14 projects involved research on guns, bringing the total spent on research in the area closer to $11.1 million.

The NIH said it continues to support research on gun violence prevention, making decisions based on factors such as public health needs and budget considerations. The studies, it said, were part of "larger efforts to develop more effective public health education programs to prevent violence." It cited examples such as parents' roles in preventing injuries, the relationship between alcohol abuse and gun violence, measures to reduce the risk of suicide among teens, and examining why war veterans have a higher risk for suicide using guns.

Dr. Garen Wintemute, who received an NIH grant to study gun violence among people who have drunken driving convictions, said that the NIH should be more explicit and could even issue a statement focusing on gun research, rather than suggesting it was interested in addressing violence generally. Scientists see a call for research as an encouraging sign to submit proposals because they're likely to get funded, he said.

"Researchers take program announcements as expressions of interest and purpose from NIH on a topic," said Wintemute, who is director of the Violence Prevention Research Program at University of California, Davis. "It is the case that the program announcement had a three-year run. That doesn't mean it had a term limit. It was up for renewal and wasn’t renewed ... The absence of renewal expresses to researchers that the interest has ebbed."

Some lawmakers say the way to propel gun violence research is to change the Dickey Amendment, which has been in place as part of a funding bill since 1996. In December, Rep. Robin Kelly, D-Ill, vice chairwoman of the House Gun Violence Prevention Task Force, and Rep. Cedric Richmond, D-La., chairman of the Congressional Black Caucus, introduced the Gun Violence Research Act. The bill would specify that federal funds may be used to study gun violence, particularly as it is related to mental health, and would mandate an annual report on gun violence from the surgeon general and a report from the Office of Minority Health. The bill does not have a Senate companion.

Former Rep. Jay Dickey, R-Ark., the amendment's author who died in 2017, said the amendment was often misinterpreted as a ban on gun violence research. Those who want to change it say it has gotten in the way of finding solutions.

“For decades, the Dickey Amendment has silenced lifesaving research and suppressed the policy dialogue around common-sense laws that can save American lives,” Kelly said in a statement announcing the legislation. “It’s time to let the science and research speak for itself so policymakers can enact the best policies to protect public safety and American families."

Though two-thirds of the 33,000 gun deaths in the U.S. are related to suicides, politicians often draw attention to gun violence after mass shootings. It isn't clear what policies would prevent the shootings. The gunman who opened fire at First Baptist Church in Sutherland Springs, Texas, had a history of violence. He was confronted by two other gun owners who may have prevented him from killing more people.

No motive was found for the gunman responsible for the mass shooting in Las Vegas. He acquired a stockpile of firearms legally but used "bump stocks" that allowed them to mimic automatic weapons. In response, the NRA and Republicans supported a change to bump stock regulations but not a legislative fix.

Trump, who delivered a keynote speech at the NRA last year, hasn't proposed a solution on gun violence prevention, but said following the Las Vegas shooting that "we'll be talking about gun laws as time goes on." He blamed mental health problems for the mass shooting in Texas.

Republicans have said in the past that the Dickey Amendment is defined narrowly enough. Recently, they have gone after policies that they believe have put guns in the wrong hands. Sens. John Cornyn of Texas, Orrin Hatch of Utah, Tim Scott of South Carolina, and Dean Heller of Nevada have cosponsored a bill with Democrats that would strengthen the federal background-check system for gun sales.

House Republicans also have blocked Democratic efforts at allowing the Centers for Disease Control and Prevention to conduct research on gun violence. The CDC's studies tend to come with recommendations, and the NRA has accused the agency of previously stepping into advocacy territory.

The NRA said it supports research in several areas, including how often firearms are used in self-defense and how guns end up in the hands of criminals. The NRA's longstanding position is that gun control laws inhibit law-abiding people and don't prevent violent crime.

"The National Rifle Association is not opposed to research that would encourage the safe and responsible use of firearms and reduce the number of firearm-related deaths," Jennifer Baker, spokeswoman for the Institute for Legislative Action at the NRA, said in an email. "Safety has been at the core of the NRA mission since its inception. However, firearm safety is not the goal of the advocates seeking government funding — gun control is. The NRA is opposed to the use of taxpayer dollars to advocate for and promote gun control."

Wintemute said researchers can study the topic and derive policies based on evidence rather than ideology.

"The people who do the research are not driven by a policy agenda," he said. "They are driven by scientific curiosity by the knowledge that firearm violence is a problem … that efforts are going to be made and those research should be based on sound evidence."