In response to this month’s shootings, Mr. Trump promptly vowed to pursue “background checks like we’ve never had before,” noting, correctly, that “there is a great appetite” for closing existing loopholes. (More than 90 percent of all voters support universal background checks.) Asserting that he enjoys “greater influence now over the Senate and over the House,” he expressed confidence that, this time, he could persuade lawmakers “to do things they don’t want to do.” He boasted, “There’s never been a president like President Trump.”

Even as Mr. Trump was touting his specialness, the N.R.A. was whispering in his ear, warning of the political Armageddon that would befall him if he crossed Second Amendment enthusiasts, even on something with such broad support as background checks. In recent weeks, the president has had multiple phone conversations with Mr. LaPierre, including while the president was on vacation at his New Jersey golf resort last week.

Right on schedule, Mr. Trump’s knees have buckled and his resolute talk has devolved into a series of (slightly garbled) bumper-sticker clichés on the theme of, “It’s people who pull the trigger, not the gun that pulls the trigger.” On his way back to Washington on Sunday, he stressed that he was “very, very concerned with the Second Amendment, more so than most presidents,” and he helpfully offered, “People don’t realize we have very strong background checks right now.” Leaning on one of the gun lobby’s favorite talking points, he said that this is “a very, very big mental health problem.”

Yes, it is — if you consider chronic political cowardice to be a mental health problem.

Now would be a particularly pathetic moment for Mr. Trump to capitulate. For all its vaunted political clout, the N.R.A. is in crisis — embroiled in legal troubles, rent by leadership squabbles and flirting with financial ruin. The president has privately voiced doubts that the group will be in a position to be a serious player in the 2020 election. What better time for him to exert his independence — to set himself apart from the political wimps?

Some White House aides have insisted that Mr. Trump is not waffling, that this is all part of a grand negotiating strategy and that he will, in fact, renew his legislative push when Congress returns from recess next month. Others have acknowledged that the president, not known for his long attention span, has lost patience and interest in the entire topic. As one told The Daily Beast, “He’s started to move on.”