After a weekend of protests and vigils following the massacre at a Florida high school that left 17 dead, President Donald Trump signaled support on Monday for bipartisan legislation aimed at improving records reporting to the federal gun background check system.

Trump’s press secretary, Sarah Huckabee Sanders, said in a statement that the president had spoken to Senator John Cornyn of Texas, a Republican, who introduced legislation intended to shore up the gun background check system last fall. “While discussions are ongoing and revisions are being considered,” Sanders said, “the president is supportive of efforts to improve the federal background check system.”

If you are looking for information on how federal background checks work, check out our explainer. For more on how the so-called Fix NICS Act might keep guns out of the hands of convicted criminals, keep reading.

What is NICS, anyway?

Launched in 1998, the FBI’s National Instant Criminal Background Check System is used by federally licensed firearms dealers to check whether a person who is trying to buy a gun is legally permitted to do so.  

When a licensed dealer calls NICS, checkers search three different databases for criminal records that might disqualify a buyer. One database, called the NICS Indices, returns an answer within minutes, and contains records that automatically disqualify a person from gun ownership.

The other two databases, the Interstate Identification Index or III and National Crime Information Center, or NCIC, contain additional criminal records. The records in those databases are used for a variety of purposes in addition to gun background checks, from traffic stops to probation reports.

Private sellers are not mandated to conduct background checks on potential buyers under federal law, but some states have added that requirement.

Why does NICS need to be fixed?

The gun background check system is only as strong as the records it contains. States voluntarily supply records to the databases that make up the NICS system, and they do a spotty job of it. Some records never make it into the databases, and others are incomplete or unclear.

The gunman who slaughtered 26 people in a church in Sutherland Springs, Texas, last  November purchased weapons legally, but should never have been allowed to do so. The Air Force later revealed that it had failed to submit criminal records to NICS that could have blocked the shooter, an Air Force veteran, from buying a gun.

The FBI has said it doesn’t know how many records go unsubmitted, but the National Rifle Association has cited a 2013 report by the nonprofit National Consortium for Justice Information and Statistics, which estimated that about 7 million records are missing. That report determined that “at least 25% of felony convictions . . . are not available” to the National Instant Criminal Background Check System maintained by the FBI.

In other cases, people are allowed to leave a gun shop with a firearm, only for a checker to later discover that they are disqualified. These are “default proceed” sales. The gunman who killed nine people at baptist church in Charleston, South Carolina, in 2015, obtained his weapons through such a purchase.

What would the Fix NICS Act do, specifically?

The bill, sponsored by Cornyn and Senator Chris Murphy of Connecticut, a Democrat, would require federal agencies to improve their reporting standards and encourage states to follow suit.

Federal agencies would be required to submit detailed action plans to the attorney general’s office, showing how they intend to upload all records on people prohibited from buying guns into the NICS database. The plans would include specific quantitative goals and timelines for compliance.

The attorney general would report the number or records, broken down by category, that each federal agency had reported.

Political appointees at agencies that did not comply would not be given annual bonuses.

States and federal agencies would be called out publicly if they failed to meet the goals they had set. They would also be given technical support as they work to build better reporting systems.

The legislation would also make $125 million available to states each year from 2018 to 2022 to improve verification of criminal records and report them to the FBI. Priority would be given to states that show they have a detailed plan for implementing better practices for record reporting.

Experts agree that the Fix NICS Act would add welcome resources and accountability to a complex and cloudy gun background check system.

Would the bill “fix” the background check system for good?

Even if Fix NICS were to become law, problems with the background check system are likely to remain.

For starters, Congress can’t force states to report more records, so there is no guarantee that they will improve their practices. The bill instead encourages compliance with direct financial incentives, as well as access to other federal assistance programs.

What’s more, the NICS background check system is complex and opaque, making it difficult for watchdogs to judge the completeness of each state’s reporting system. Of the three FBI databases that states enter their records into, the FBI only publishes data for one, the NICS Indices.

How might a strengthened background check system prevent crime?

Preventing more people with criminal records from buying guns will almost certainly be a benefit to public safety. Whether or not the specific changes being proposed will prevent future mass shootings is murkier.

It is unlikely that improvements to the FBI’s gun background check system would have prevented the Parkland shooter from buying the semiautomatic AR-15 rifle he used in the mass killing. According to the Bureau of Alcohol, Tobacco, Firearms and Explosives, the gunman was not prohibited from gun ownership and purchased the gun legally.

An airtight background check system would have prevented the shooters Sutherland Springs and Charleston from obtaining the weapons they used in the attacks. But prohibited buyers can still often find ways around the system by buying guns in private sales or on the black market.

What are the odds that background check reform will actually happen?

With widening calls for the president and Congress to act to stop mass shootings, the Fix NICS legislation, which was backed by the NRA, seems to have the best chance of any existing bill of being signed into law.

In a Tweet Monday, Murphy said Trump’s support is a sign that the politics of gun violence are shifting. But, he added, “No one should pretend this bill alone is an adequate response to this epidemic.”