U.S. Rep. Patrick Murphy joined other Democrats in demanding the House take up a bill that would keep people on the FBI’s watch list from buying guns, saying far too many people on the list have been allowed to get firearms.

Murphy tweeted a graphic on Dec. 8, 2015, claiming that "91 percent of suspected terrorists who attempted to buy guns in America walked away with the weapon they wanted."

His tweet came after Republicans repeatedly blocked a bill that would keep people on the FBI list from buying guns. In an unusual procedural move, Murphy and other Democrats signed a petition to bring the bill to the House floor, but it currently doesn’t have the required 218 signatures for further action. The Senate earlier in December struck down a similar bill.

We were curious if Murphy -- who is also running in the Democratic primary for U.S. Senate in 2016 -- was right to say that 91 percent of suspected terrorists looking to buy guns were able to get one. Our research showed that is accurate by the best available estimates, but there are some caveats about the watch list we should keep in mind.

Watching the watch list

The FBI maintains what is informally known as the terrorist watch list through its Terrorist Screening Center, which maintains a consolidated file of "those known or reasonably suspected of being involved in terrorist activity."

As you can imagine, some critics are uneasy about the government maintaining any sort of list designating people potential enemies of the state, but it’s generally considered a valuable tool for national security. The Democrats’ bill allows for cross-referencing the list while conducting a background check for a firearm purchase.

The actual size of the list and who is on it is not public information, but we have estimates: In 2011, an FBI fact sheet said there were 420,000 people on the list. Current estimates have put the list at around 700,000. Since the database pulls information from U.S. and global agencies, only a relative handful — about 8,400 in 2011 and likely around 10,000 now — are American citizens or legal residents.

Murphy’s stat comes from a March 2015 report from the U.S. Government Accountability Office, which examined how many people applying for gun purchases were run through the FBI’s instant background checks and also were on the watch list.

Between February 2004 (when the FBI started keeping tabs on people on the list trying to buy guns) and December 2014, there were 2,233 people on the list who applied to buy a weapon. Of those, 2,043 were allowed to proceed, including three applications to buy explosives. That’s a bit more than 91 percent.

Experts have told PolitiFact that the GAO report is plausible, and not really that remarkable, considering how many gun purchases Americans have made in the past decade. But there are things to keep in mind.

The data show how many weapons applications there were, not how many individuals, so one person could have potentially made several purchases. The report also didn’t show transactions made at gun shows, where federal background checks aren’t conducted, so the number actually could be higher.

There also have been some issues with the terror watchlist database in the past.

A 2009 U.S. Justice Department audit showed that 35 percent of the people on the list were "associated with FBI cases that did not contain current international terrorist or domestic terrorism designations" and should have been removed from the list.

There also are multiple entries for slight variations of the same name, which has previously led to people with the same name as a person on the watch list being stopped at airports, a problem that experts say has largely been resolved.

Our ruling

Murphy said, "91 percent of suspected terrorists who attempted to buy guns in America walked away with the weapon they wanted."

His figure comes from a GAO report that showed a bit more than 91 percent of gun store weapons applications by people on the FBI’s terrorist watch list were approved. There are some caveats to the watch list, including past issues with who is included and why. The report also didn’t distinguish how many individuals are making these applications, or how many people on the watch list potentially buy firearms at gun shows.

But experts have told us the report is both plausible and not altogether unsurprising, given how many guns Americans purchase. We rate Murphy’s statement Mostly True.