Correction: An earlier version of this editorial incorrectly described Sen. John McCain as representing Nevada. He represents Arizona. The following version has been updated.

A COWARDLY minority of senators blocked a gun background-check proposal on Wednesday, in one vote betraying both the will of the American people and the charge voters gave them to work in their interest. But at least those senators avoided a rebuke from the National Rifle Association.

Expanding background checks on would-be gun buyers is an idea that almost everyone endorses, because it’s an obvious thing to do. It doesn’t infringe on Second Amendment rights. It doesn’t restrict what weapons people can buy, as an assault-weapons ban or restriction on large-capacity magazines would. It closes some glaring loopholes in the system that are more than a decade old, loopholes that allow people to buy vast quantities of deadly weapons at gun shows and on the Internet without having their names checked against mental health and criminal records. Ninety percent of Americans support this reform.

The proposal before the Senate on Wednesday would not even have required a background check before every gun transfer. Sen. Joe Manchin III (D-W.Va.) and Sen. Patrick J. Toomey (R-Pa.) had worked out a compromise that would have allowed person-to-person gun transfers in non-commercial settings to occur without scrutiny. But, along with new measures to crack down on “straw purchases,” the plan would have helped keep guns from those who should not have them. The proposal was, in other words, the very least — the bare minimum — that lawmakers could do to prevent more guns from ending up in the wrong hands.

Yet most Republicans and a handful of Democrats — Max Baucus (Mont.), Mark Begich (Alaska), Heidi Heitkamp (N.D.) and Mark Pryor (Ark.) — couldn’t locate enough backbone even to vote for the bare minimum.

Perhaps most insulting was the bizarre conspiracy theories on which many of the opponents grounded their disapproval. Sen. Ted Cruz (R-Tex.), for example, claimed that passing the ­Manchin-Toomey plan would put the country “inexorably on the path to a push for a federal registry.” Yet the proposal specifically outlawed any national gun registration scheme — and federal authorities wouldn’t have been allowed to keep background-check records.

On the Senate floor, Sen. John McCain (R-Ariz.) spoke of the political courage of Mr. Manchin and Mr. Toomey. Also on the list is Mr. McCain himself, who pushed against the political head winds to vote for the proposal, along with Susan Collins (R-Maine), Mark Kirk (R-Ill.) and red-state Democrats Kay Hagan (N.C.) and Mary Landrieu (La.). Though it seems odd to call what should have been an easy vote a courageous one, 46 of their colleagues failed that test.

Following Wednesday’s vote, President Obama said the episode was “just round one,” and he promised to keep pushing on gun policy. But it’s now unclear — at best — whether the Senate will manage to pass any gun legislation at all in the year following the murder of 20 children in Newtown, Conn., a tragedy that followed the carnage at an Aurora, Colo., theater, which was not so long after the mass shooting involving former representative Gabrielle Giffords in Tucson. Maybe more background checks and tools to fight gun trafficking wouldn’t have stopped all of these tragedies. But they could prevent another — and cut back on the horror of everyday gun violence that afflicts this country.