A strange thing happened after 45 senators killed a bill to expand background checks for gun buyers five weeks ago: many of those same senators suddenly discovered a profound affection for background checks. They had been for them all along, it turns out, and wanted nothing more than to keep guns out of the hands of felons.

“Knowing your interest in gun control, I wanted to give you an update on legislation I have co-sponsored and supported recently,” Senator Dean Heller, Republican of Nevada, wrote to his constituents earlier this month. “I have been adamant from the beginning of the gun control debate that our current background check system needs strengthening and improving.”

Mr. Heller says he was a co-sponsor of a bill called the National Instant Criminal Background Check System Reporting Improvement Act. He doesn’t explain that the bill would have made it easier for people involuntarily committed to mental institutions to own guns. And nowhere does he mention that he actually voted against a far more important proposal, sponsored by Senators Joe Manchin III and Patrick Toomey, that would have required background checks for buyers at gun shows and over the Internet.

That bipartisan measure would have closed a gap that has let millions of guns get into the wrong hands. At the time, Mr. Heller said he voted against it because it would have led to the creation of a gun registry, though the bill would actually have made such a registry explicitly illegal.