The president himself could be another factor. Historically, public opinion on guns — and other issues — tends to shift against the preferences of the party in power. Public support for gun control laws slipped when Barack Obama became president and has tended to increase since his exit from office.

But even in the Trump years, public support for new gun laws has generally remained beneath the levels of the George W. Bush years or the 1990s, when Congress passed an assault weapons ban. Polls over the coming weeks may show support for new gun laws reaching even higher levels, as they did after the high school shootings last year in Parkland, Fla.; for now, public opinion looks more the way it did during the Obama years, when gun legislation stalled.

Mr. Trump’s support for gun laws, should it endure, may be a larger factor than the small shifts in public support.

The challenge of polling on guns

Polls repeatedly show overwhelming support for background checks on gun purchases. They are favored by Democrats and Republicans, and among Americans who own guns and those who don’t. But ballot measures proposing expanded background checks did not result in resounding victories in 2016 in two states that tend to vote Democratic, Maine and Nevada. The measure passed by less than a point in Nevada and failed in Maine, even among the voters who chose Hillary Clinton over Mr. Trump on the same ballot. A “no” against background checks received more votes than Donald J. Trump did in both states.

The wide gap between national polls and the results of state ballot measures illustrates the challenge of measuring public opinion on specific issues. And the ability of gun activists to whittle down support for gun control in a heated political debate raises doubts about whether the polls reflect strongly held public demands for action, as activists suggest, or weakly held views that Republicans and their allies could change.

Democrats have faced the danger that gun owners were likelier to cast ballots based on the issue than the potentially larger group of Americans who support gun control but perhaps not as passionately. It has been a costly trade for Democrats in the relatively white rural areas where the party has traditionally counted on the support of working-class gun owners.

As recently as last year’s midterm elections, many Democratic candidates who tried — and often succeeded — to win white working-class Democratic areas, like Conor Lamb in Pennsylvania, played down the need for an assault weapons ban after Parkland. These Democratic concerns are far more pronounced than they were a decade ago.