WASHINGTON — Senator Joe Manchin III, Democrat of West Virginia, was at a loss on Tuesday. After the massacre of children at Sandy Hook Elementary School in 2012, he challenged the pro-gun bent of his state and co-authored legislation to expand background checks of gun purchasers, only to see the measure fail.

“I just think that common sense has to prevail,” a dispirited Mr. Manchin said, explaining why he thinks that now is “the wrong time” to revive his bill. “But until that happens, until other people feel the same, we’re at a stalemate and that’s a shame.”

For years, amid a string of mass shootings in places whose names are by now seared into the national psyche — Columbine, Aurora, Virginia Tech, Newtown, San Bernardino, Orlando and now Las Vegas — Democrats have tried to enact what they call “common-sense” gun restrictions. Time and time again, they have failed.

This week’s massacre in Las Vegas, which killed at least 59 people and injured more than 500, appears to have done little to change Washington’s gun control dynamic.