Last Valentine’s Day, a year ago this Thursday, classes were wrapping up at Marjory Stoneman Douglas High School when a former student with a semiautomatic rifle murdered 17 people and wounded 17 others.

It so happens that this Wednesday, the House Judiciary Committee will move to advance legislation requiring background checks on all firearm sales. The killer in the Parkland, Fla., school massacre passed such a check, but this measure would close a loophole exploited by other killers that exempts unlicensed gun sellers from conducting background checks. Support for such a change is overwhelmingly popular, even among gun owners. The bill has an excellent chance of passing the Democrat-led House. Its prospects in the Senate, controlled by the Republican majority leader, Mitch McConnell, are bleak.

Even so, the very emergence of this bill is a reminder of how the gun debate has shifted since President Trump took office — and not in a direction that Second Amendment crusaders might have hoped. Politically, financially and legally, the gun-rights cause and, more specifically, the lobbying juggernaut that is the National Rifle Association have not fared well in the Trump era. If this trend continues — or accelerates — it could wind up being a rare silver lining to Mr. Trump’s presidency.

Some of the challenges facing the gun lobby are not specific to Mr. Trump. A gun-loving president always makes a less effective boogeyman than a gun-skeptical one. In that way, President Barack Obama was good for the gun-rights cause — and it was perhaps inevitable that, having labored to get Mr. Trump elected, the N.R.A.’s fund-raising would taper off. In 2017, the group’s revenues dropped by $55 million, or 15 percent, over its 2016 haul, driven largely by a decline in member dues. Combined with its heavy spending in the 2016 campaign, the group now finds itself in a deep financial hole, in debt to the tune of $31.8 million.

The N.R.A. has suffered Trump-specific turmoil as well. As part of the investigation into Russian meddling in the 2016 presidential election, the special counsel, Robert Mueller, has been exploring possible ties between the N.R.A. and Russia. Among Mr. Mueller’s top concerns is reportedly whether Russian interests funneled money to the Trump campaign via the N.R.A. — and, if so, to what degree the group’s leaders may have known what was happening.

In addition to Mr. Mueller’s interest in the N.R.A., there have been multiple congressional inquiries into a possible love triangle among the gun group, Team Trump and Russia. With Democrats now in charge of the House, expect the scrutiny to get more intense. Representative Adam Schiff, the new head of the Intelligence Committee, has said that under Republican leadership the committee did not delve deeply enough into the muck. “We were really not able to determine how the Russians used the N.R.A. as a back channel or look into allegations that the Russians may have funneled money through the N.R.A. to influence the election,” Mr. Schiff recently told The Times. “Those issues remain of deep interest to us.”

Beyond any legal missteps that may be uncovered, revelations that the N.R.A. was snuggling up to Russian officials and intimates of President Vladimir Putin already have proved a public-relations nightmare. Particularly embarrassing is the bizarre case of Maria Butina, the Russian graduate student who pleaded guilty in December to working as a foreign agent and who conspired to infiltrate the N.R.A. and the Republican Party in order to help Russia influence American politics.

While the Russia-N.R.A. bonds were years in the making, Americans can thank Mr. Trump for the intense spotlight on this unwholesome relationship.

Last year, for the first time in nearly two decades, polling indicated that more Americans held a negative view than a positive view of the N.R.A. There has also been an upswing in support for stricter gun laws.

Despite the will of the people, the Republican-controlled Congress clung to its do-nothing approach after the Parkland shooting and others like it. At the state level, however, there has been action. The private sector also got involved. Dick’s Sporting Goods and Walmart both halted the sale of assault-style weapons in their stores, along with the sale of guns and ammunition to customers under age 21. Companies ranging from MetLife to Delta to Alamo Rent A Car did away with discounts for N.R.A. members.

The political world has sensed this shift in the wind. Of late, more lawmakers have seemed willing to boast about their poor ratings by the gun lobby. The 2018 elections were the first in which spending for gun-safety advertising exceeded that for guns-rights ads, and candidates backed by gun-safety groups enjoyed important victories.

Not all of the change can be directly attributable to Mr. Trump, of course. But, much as women’s frustration over his presidency helped drive the #MeToo movement, his administration has energized gun-safety advocates, who have put the gun lobby and its cause on the defensive.

This won’t yield an imminent revolution on regulating firearms, especially within the overly cautious halls of Congress. The N.R.A. remains a political powerhouse, an increasingly conservative Republican Party still controls the White House and the Senate, and guns remain a centerpiece of the culture war.

But with a topic this polarizing, small steps deserve to be applauded — and encouraged. When lawmakers held a hearing on the background-check bill last week, it was the first hearing in eight years to broach the subject of gun violence.

With a little luck and some political spine, more such actions will follow. The victims and survivors of Parkland, and of the 339 other mass shootings in 2018 alone, deserve more than pious sentiment and political cowardice.

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