Eight months before Election Day, Donald J. Trump was about a half-hour into his stump speech at a convention center in Louisville, Ky., when several protesters interrupted his rally. “Get ’em out of here!” he bellowed in response.

Matthew Heimbach, a white nationalist wearing a red “Make America Great Again” hat, gave a hard shove in the back to Kashiya Nwanguma, a black college student who had been holding up a poster depicting Mr. Trump’s face on the body of a pig.

“He knew what he was asking for,” Mr. Heimbach said recently of Mr. Trump’s remark.

What Mr. Trump got was a pair of lawsuits: one filed by Ms. Nwanguma and the other by one of Candidate Trump’s most fervent young admirers among the white nationalist movement, Mr. Heimbach.

Two months after the March 2016 rally, Ms. Nwanguma and two other protesters sued Mr. Trump, the Republican presidential candidate, contending incitement, saying he was legally liable because Mr. Heimbach and other Trump supporters were acting as his “agents.” The civil suit also accuses Mr. Heimbach and two other Trump supporters of assault and battery, adding that they shouted racial slurs at her.