One of those mistakes came at the beginning of his campaign for expanded background checks, at a breakfast on March 18 for reporters and columnists sponsored by Bloomberg View in New York City.

At the meeting, Manchin accidentally let slip that he was headed the next day to a meeting with the National Rifle Association to try to woo the powerful gun lobby’s support for his legislation, which at the time had yet to gain a Republican co-sponsor.

Although no ground rules had been set at the start of the Bloomberg discussion, Manchin retroactively tried to put his comments off the record. The senator’s office was then forced to spend the rest of the morning on the phone with reporters pushing back against the terms, including one from BuzzFeed. But Manchin’s talks with the NRA leaked later that week to Politico.

The senator’s weeks of negotiations with the NRA came to a halt last week on the day he and Toomey unveiled their bill at a press conference. The press secretary in Manchin’s office told BuzzFeed that morning that the NRA was staying “neutral” on the bill. But minutes after the story was published and the press conference concluded, the NRA released a statement disavowing background checks. The group’s spokesman, Andrew Arulanandam, later went even further: “We are opposed to Toomey-Manchin. Period,” he said. …

By the morning of the vote, their relationship was in apparent disarray: The NRA was asking its supporters to call their representatives to “urge them to oppose the Manchin-Toomey amendment,” and Manchin was on the floor of the Senate, saying the group had misrepresented his bill to the public.