Educators still reeling from gun violence that left 17 dead at a Florida high school expressed frustration Thursday at President Trump’s call for teachers to take up arms to defend their classrooms against school shooters, saying the thought of using lethal force in a crowded hallway or against one of their students was unimaginable.

They wondered about scenarios in which they could face shooters on a hectic campus — or even, potentially, draw a gun to confront an armed and dangerous student.

“There’s no way I would do that,” math teacher Jim Gard said of Trump’s proposal. “I would retire.” Gard teaches at Marjory Stoneman Douglas High School in Parkland, Fla., where 17 people were gunned down on Valentine’s Day. He barricaded students in his darkened classroom last week while bullets flew. Policymakers, he said, “need to do their job and control guns first.”

“If it gets to the point where we have to arm our teachers, then we have completely failed, completely failed as a society,” Gard said.

Trump described the proposal in two emotional White House meetings Wednesday and Thursday, when he convened public officials, school leaders and Stoneman Douglas students to talk about school safety. The president also has talked about banning bump stocks, expanding background checks and bolstering mental health resources.

But the majority of his comments on school safety have been focused on arming a significant portion of the educator workforce — between 10 and 40 percent of teachers — using federal resources. He said military veterans who teach would be prime candidates for these roles.

“We have to harden our schools, not soften them,” Trump said during a White House meeting Thursday. “I think a concealed permit for teachers and letting people know there are people in the building with a gun . . . you won’t have these shootings. Because these people are cowards. They’re not going to walk into a school if 20 percent of the teachers have guns.”

Trump left out critical details when he discussed the proposal — such as how it would be funded, how many teachers would be armed and trained, and whether schools would be mandated to train teachers. But school security decisions are typically the purview of states and school boards. Exactly how the federal government would carry out the proposal in schools is unclear.

As school shootings made headlines year after year, many schools hired police officers or armed guards to patrol campuses with the help of federal money, making them a fixture in American schools. About 57 percent of public schools in the 2015-2016 school year had security staff on campus at least once a week and nearly 43 percent were patrolled by armed law enforcement officers, according to federal data.

Outside of anecdotal data, it is unclear how effective they have been at deterring or halting school shootings. Critics say their presence has led to greater numbers of student arrests for minor behavioral infractions, particularly among minorities.

The National Association of School Resource Officers rejected Trump’s proposal to arm teachers, saying the solution is to put police officers with special training in every school. Only a sworn law enforcement officer should be responsible for carrying firearms in a school, said Mac Hardy, director of operations for the association. He noted that a school shooting poses a “frantic, incredibly stressful situation” that requires intensive training.

But Trump said existing school security personnel are inadequate, particularly for a massive campus such as Stoneman Douglas.

“You can’t hire enough security guards,” Trump said.

There was at least one armed deputy on campus when the shots were fired last week, but the Broward County sheriff’s office disclosed Thursday that the deputy remained outside the building as students ran for their lives. The deputy has resigned and retired.

School security experts say the best defense against a school shooting are preventive measures intended to identify troubled students and intervene before they turn violent, not putting guns in the hands of teachers. The Trump administration has proposed gutting the education budget, including paring back one source of funding for mental health resources in schools.

“The proposal to arm teachers might be emotionally appealing after a school shooting, but it is not practical or realistic,” said Dewey Cornell, a University of Virginia professor who studies school safety. “We should place more emphasis on preventing shootings than preparing for shootings. Prevention must start long before a gunman shows up at school. Instead of more guards, we need more counselors.”

The proposal is unlikely to get traction in Congress, where some members of the president’s party have already rejected it. It would be costly and time-consuming to train just 10 percent of the educator workforce. With 3.2 million teachers in public schools and 400,000 in private schools, it would mean preparing and arming 360,000 to 1.4 million educators.

But teachers said they believed it could make their campuses far more dangerous because of the chance that they could hit an innocent bystander or that a student could grab their gun. Teniea Sandlin, 45, a sixth-grade teacher at Parkside Elementary School in Des Moines, Wash., disputed Trump’s assumption that armed teachers would stop a shooter.

“I don’t think it’s going to be much of a deterrent to a suicidal maniac,” she said. “It’ll be just dangerous for the school-age population. . . . What kind of country do we want to live in, where schools are war zones?”

Kirk Bast was chairman of the counseling department at Arapahoe High School in Colorado, where a student killed a classmate and then himself after being cornered by an armed sheriff’s deputy in the library in 2013. Bast barricaded himself in a room and grabbed a tripod, preparing to bludgeon an armed intruder. But at no point did he wish he had a firearm.

“It’s a risk,” said Bast, who retired in 2016. “I think about accidental death with that. I think about a kid grabbing the gun when nobody’s looking.”

But John Brown, a 30-year-old substitute teacher in Minneapolis and a gun owner, said that in light of recent events, a version of Trump’s idea might be worth exploring.

“Sitting in a corner and waiting to die is not a plan,” he said. “We have to have something else.”

A few school districts across the country permit teachers to carry firearms and at least one state, Texas, permits school districts to arm teachers. Following the Florida shooting, an Alabama lawmaker has proposed that teachers be permitted to carry arms at school after a 40-hour training. But Hardy, of the school resource officer association, criticized the plan as inadequate to prepare teachers.

“Wow, that scares me to death,” Hardy said. “Shooting a handgun is not easy.”

David Thweatt, superintendent of the Harrold Independent School District in Texas, began thinking more seriously about school security after a man killed five girls in an Amish schoolhouse in Pennsylvania.

All 115 students in the Harrold district attend school on one remote campus in North Texas, and it could take up to 30 minutes for a sheriff’s deputy to reach them during a school shooting. So Thweatt decided to arm school personnel.

“What do I do with an active shooter in my school? I needed to answer that. We wanted to protect our kids,” he said. Since members of his staff have been trained and armed, staff have had to use weapons only on roaming wildlife that posed a threat, including feral pigs, rattlesnakes and rabid skunks.

Thweatt said arming teachers might not be practical everywhere, but he believes it is something all school districts should seriously consider.

Clayton Allen, a former Army medic who conducts the orchestra at Lake Braddock Secondary School in Fairfax County, said he believes school resource officers are probably best equipped to respond to school shooters. But Allen, who regularly trains with firearms as a member of the D.C. National Guard, said if he were asked to step up to protect his students, he would.

“I would do anything to protect my kids and my school and these schools,” Allen said.