Donald Trump's promise to make concealed carry permits valid across state lines gained traction when the Republican-led House passed a bill in December that would treat gun permits similarly to driver's licenses.

But the measure faces long odds in the Senate.

Under the broad strokes of the House-passed Concealed Carry Reciprocity Act, having a permit issued by one state would make it legal to carry in any state. This would streamline the patchwork of varying laws and standards across the country currently in place as a result of each state having largely determined its own scheme for regulating the carrying of firearms.

Thirty-eight states require gun owners to obtain a state-issued permit before they can lawfully carry a concealed weapon in public, while a dozen states require no permit at all.

States also have traditionally decided for themselves whether to honor out-of-state permits, a legal concept known as "reciprocity." But the NRA-backed measure would establish a national reciprocity scheme as the new law of the land.

Then-candidate Trump appealed to Second Amendment voters in part on a promise to secure recognition for concealed-carry permits in all 50 states.

"The right of self-defense doesn't stop at the end of your driveway," Trump's campaign literature stated. "That's why I have a concealed carry permit and why tens of millions of Americans do, too. That permit should be valid in all 50 states."

The Republican-sponsored bill cleared the House on Dec. 6 in a 231-198 vote that broke mostly along party lines. That marks progress toward Trump's promise — but only to a degree.

The bill faces a steep climb in the Senate, where Republicans hold a slim 51-49 majority, short of the 60 votes needed to break a filibuster by pro-gun control Democrats.

Sen. Chris Murphy, D-Conn., who emerged as a leading advocate for stricter gun regulation following the 2012 mass shooting at Sandy Hook Elementary School, condemned the House-passed measure as "a terrible, dangerous idea."

"I urge leaders in Congress to dump the national concealed weapons bill and work together to keep deadly weapons away from people we all already agree shouldn't have them," he wrote in a press release.

While the House's passage of the GOP concealed carry reciprocity bill marks progress toward Trump's promise, the measure faces opposition in the Senate, where Republicans lack the votes needed to break a Democratic filibuster. For now, we rate this promise In the Works.