(The Hill) — A gun control group on Thursday sent a mile-long convoy of 52 buses to the home of Sen. Ted Cruz (R-Texas) and filled the empty seats of the lead bus with the personal memorabilia of children who have died during school shootings.

The organization, Change the Ref, said the fleet of buses — part of a movement called The Yellow Bus Project —traveled to Cruz’s home in Houston, where founders Manuel and Patricia Oliver left a hand-written letter for the GOP senator, who was not home.

The letter was written by the Oliver’s late son, Joaquin, who was among the 17 students who died in the 2018 high school shooting in Parkland, Fla. Joaquin Oliver wrote the letter to Cruz when he was 12 years old, urging the senator to support universal background checks.

On Wednesday, the bus convoy assembled to park in the shape of an assault rifle in Houston before the fleet traveled to Cruz’s home on Thursday morning.

Manuel Oliver said the empty seats on the 52 buses represented the 4,368 children who have died from gun violence since 2020, becoming the leading cause of death for children in the U.S.

Oliver said Cruz is the leading recipient of donations from gun lobbyists, such as the National Rifle Association (NRA), in Texas. According to the money-tracking organization Open Secrets, Cruz has collected $749,000 from gun rights groups over the course of his career.

“To commemorate this horrific historic moment, we are showing American voters the toll these politicians have taken on our children’s lives with this all-too-real archive,” Manuel Oliver said in a statement. “And this is only the beginning. We will not stop with Sen. Ted Cruz. To every politician who has stood by, taken NRA money, and refused to listen to the people they represent: the museum is on the way to honor you next.”

The mile-long bus convoy is called the NRA Children’s Museum.

Texas is still recovering from a deadly mass shooting in May, when a gunman opened fire inside an elementary school in Uvalde and killed 19 children and two adults.

Days after the shooting, Cruz attended an NRA convention and blamed video games, social media bullying and poor church attendance for the rise in gun violence.

Congress recently passed into law bipartisan legislation on gun control that extended background checks for adults under 21 and poured billions into mental health services and school safety. Cruz was among the 33 Senate Republicans who voted against the law.

Change the Ref, which Manuel and Patricia Oliver formed after they lost their son in the Marjory Stoneman Douglas High School shooting, is pushing for Congress to pass a law mandating universal background checks to cover unlicensed dealers and other loopholes.

Patricia Oliver said she wants “voters to remember which politicians are in the pocket of the NRA when they visit the polls in November.”

“We urge everyone to join us in our mission to fight for every innocent soul lost to gun violence and to demand universal background checks on gun sales,” she said in a statement.