President Trump — under pressure from angry, regretting students from a Florida high school where a gunman killed 17 people last week — ordered the Justice Department on Tuesday to problem regulations banning so-called bump stocks, which convert semiautomatic guns into automatic weapons like those utilized last year in the massacre of concertgoers in Las Vegas.
A day earlier, Mr. Trump signaled that he was open to supporting legislation that would humbly improve the national gun background check system, and on Tuesday night, he posted on Twitter that Democrats and Republicans “must now focus on enlarging Background Checks!”
But Mr. Trump’s first embrace as president of any gun control measures was dismissed by gun control supporters as minor. The National Rifle Association supports the background check legislation and also backs bump stock regulation, although not an outright ban.
Speaking at the White House days after a shooting at Marjory Stoneman Douglas High School, Mr. Trump said that he had directed Attorney General Jeff Sessions to develop the regulations.
“We cannot merely take actions that make us feel like we are creating a difference,” Mr. Trump said at a ceremony as he conferred the medal of valor on public safety officials. “We must actually make a difference.”
In Florida on Tuesday, the Republican-controlled State House rejected an effort to instantly consider a bill to ban big-capacity magazines and the type of assault rifles utilized in last week’s attack, even as students from Stoneman Douglas High School watched from the gallery.
The party-line vote was on an unusual procedural motion offered by a Democrat, and Republican leaders were critical of the effort to force a vote. They said they would consider other gun control bills before the session ends in March, but none of those measures is expected to go as far as banning assault rifles.
At the White House, Sarah Huckabee Sanders, the president’s agent, said the president was determined to find ways to protect Americans, and especially children, from gunmen. Asked about a broader ban on assault weapons, Ms. Sanders said the White House has not “closed the door on any front.”
Despite the day’s developments, there was deep skepticism in Washington that anything would change because of the long history of inaction by state and federal politicians after familiar mass shootings. Gun control activists said they were braced for another disappointing battle with lawmakers.
The president, they noted, promised unwavering fealty last year to the National Rifle Association, drawing thunderous applause at its annual convention by declaring, “To the N.R.A., I can proudly say I will never, ever let you down.” The group in turn enthusiastically endorsed Mr. Trump and spent $30 million on his campaign.
Senator Christopher S. Murphy, Democrat of Connecticut, who sponsored the newest background check measure with Senator John Cornyn, Republican of Texas, said he was unimpressed by Mr. Trump’s openness to it. “Let’s not pretend this is some big concession on his part,” he said. “If this is all the White House is willing to do to address gun violence, it’s wholly insufficient.”
The background check bill, which searches to improve the existing database utilized to secure gun purchases by criminals and the mentally ill, is a small nod in the direction of gun control that does nothing to close loopholes that allow millions of gun sales without a background check. Last year, N.R.A. officials said they were fine with it.
It is also unclear whether Mr. Trump’s statement of support for the measure, which included a desire for some “revisions,” might be linked to other legislation that the N.R.A. backs. In the House, a familiar background check measure was combined with legislation that would effectively allow people to constitutionally carry concealed weapons in all 50 states.
That legislation is the top priority for the N.R.A., and gun control activists have promised to fight it aggressively.
“That normalizes the carrying of guns on all American streets,” said John Feinblatt, the president of Everytown for Gun Safety, a group that advocates gun control measures. He said joining the two measures would be a “craven” bait-and-switch and “disrespectful for all the families” of the Florida school that suffered through last week’s shooting.
The president’s bump stock briefing surprised the Bureau of Alcohol, Tobacco, Firearms and Explosives, which did not come to have been informed of the pending remarks from Mr. Trump. The Justice Department declared a review of the devices in early December. Led by the A.T.F., the review sought to describe whether the bureau — which is responsible for policing firearms — was capable to regulate the devices without action from Congress.
Under the Obama administration, the bureau had described it could not regulate them. Given that prior position, A.T.F. officials had indicated privately in the months after the Las Vegas massacre that any ban of bump stocks would need new legislation.
Bump stocks were not utilized on the rifle in the shooting last week in Florida, the authorities said.
Mr. Trump’s announcement on Tuesday came to short-circuit the agency’s review. The A.T.F. had not yet determined whether it had the authority to ban the gadgets when Mr. Trump directed Mr. Sessions to draft a regulation doing so.
In a statement, an A.T.F. official said she was “not authorized to comment on pending legislation, legislative proposals or the probability of executive action.” A Justice Department agent said that the department “understands this is a priority for the president.”
The shooting in Florida prompted the White House to highlight the administration’s actions as students from the school included Mr. Trump among the politicians they criticized for failing to keep them safe.
In an impassioned speech on Saturday, Emma Gonzalez, a senior at the school, bashed the president’s N.R.A. ties and accused him of setting a crass monetary value on the lives of gunshot victims by taking so much money from the gun-rights group.
“If you don’t do anything to secure this from continuing to occur, that number of gunshot victims will go up and the number that they are worth will go down,” Ms. Gonzalez said on Saturday at a rally for gun control. “And we will be worthless to you.”
With funerals underway for those who died at the Florida high school, Mr. Trump said that he plans to host a “listening session” on Wednesday with high school students and teachers at the White House. He is scheduled to meet on Thursday with state and local officials to discuss school safety.
Ms. Sanders told reporters on Tuesday that the session on Wednesday will include students and parents from the Florida school as well as people affected by school shootings at Columbine High School in Colorado and Sandy Hook Elementary School in Newtown, Conn. She did not say whether any of the student activists who have been critical of Mr. Trump were invited to the White House.