It has been 38 days since the mass shooting at Marjory Stoneman Douglas High School in Parkland, Fla.; 174 days since the shooting at a concert in Las Vegas; 1,011 days since the killings at a church in Charleston, S.C.; and 1,926 since the tragedy at Sandy Hook Elementary School. Ten days ago, students organized a nationwide school walkout to demonstrate their outrage about these and other shootings.

On Saturday they plan to amass in Washington to pressure a Congress that has done nothing meaningful to protect American children in classrooms, movie theaters, churches, malls — because, thanks to the National Rifle Association, many of their elected representatives are too busy protecting their re-election.

My advice to the students? When you finish marching on the mall, march into the specific congressional districts where you can actually make a difference.

The midterm elections are in eight months. A vast majority of congressional districts have been gerrymandered bright blue or ruby red. In those deep-red districts, the only threat that far-right members of Congress face is a primary challenge from someone farther to the right. You may regard voting for universal background checks as a no-brainer, but they see it as a blemish on their N.R.A. rating — an open door to a primary challenge. That explains the unmovable fealty these representatives have to the gun lobby.