Three headliners pulled out of this week’s N.R.A. convention, citing Uvalde.

Several musical performers who planned to appear at this week’s National Rifle Association convention in Houston have withdrawn out of respect for the victims of the massacre in Uvalde, 279 miles west of the typically boisterous annual gun-rights gathering.

Don MacLean, the 76-year-old folk-rock singer who wrote and performed the iconic “American Pie,” told People Magazine on Thursday that the mass shooting, which killed 19 children and two teachers, had compelled him to scrap his planned appearance.

“In light of the recent events in Texas, I have decided it would be disrespectful and hurtful for me to perform for the N.R.A. at their convention in Houston this week,” Mr. McLean told the magazine.

Rank-and-file N.R.A. members, along with journalists, began streaming into the George R. Brown Convention Center late Thursday, for a three-day convention scheduled from Friday through Sunday. Seldom has the conclave, often a chest-thumping gun-rights rally, been held under such strained circumstances, amid internal strife, in the shadow of mass murder.

The convention was planned months ago, before a recent spate of mass shootings, including the killings in Uvalde, and a racist attack on a supermarket in Buffalo earlier this month that left 10 people dead. Both gunmen used AR-15-type semiautomatics that have been legal since the expiration of the assault weapons ban in 2004, a big N.R.A. victory.

“Our deepest sympathies are with the families and victims involved in this horrific and evil crime,” the N.R.A. said on Twitter on Wednesday.

That was not enough for some would-be attendees.

Larry Gatlin, a member of the pop-country trio the Gatlin Brothers, said the massacre convinced him that the country needed to impose more stringent background checks on gun buyers.

“While I agree with most of the positions held by the N.R.A., I have come to believe that, while background checks would not stop every madman with a gun, it is at the very least a step in the right direction toward trying to prevent the kind of tragedy we saw this week in Uvalde — in my beloved, weeping Texas,” Gatlin said in a statement.

Larry Stewart, another country singer, said on Twitter that he too would skip the convention “to honor the victims, families, the town and our friends in Texas.”

The event’s political keynoters — Gov. Greg Abbott of Texas, Senator Ted Cruz and Gov. Kristi Noem of South Dakota — all plan to attend. Former President Donald J. Trump is scheduled to appear on Friday, although those in attendance will be prohibited from carrying firearms to his speech by the Secret Service.

The events in Uvalde have spurred an influx of demonstrators, including a planned joint appearance by the leaders of the nation’s two largest teachers’ unions.

Becky Pringle, president of the National Education Association, and Randi Weingarten, president of the American Federation of Teachers, are expected to speak on Friday morning.

Two teachers who survived other high-profile school shootings in recent years are expected to join them: Sarah Lerner, a teacher at Marjory Stoneman Douglas High School in Parkland, Fla., in 2018, and Abbey Clements, a teacher at Sandy Hook Elementary in Newtown, Conn., in 2012.

Both unions have opposed arming teachers.

In a joint news release, the unions — which represent nearly 5 million teachers, educators and school employees nationwide — condemned the N.R.A. and demanded that the group “loosen their chokehold” on federal gun policy.