This is a strange year politically. But there is some precedent to wild protests at Presidential candidate appearances.
In 1967-68, with the Vietnam War raging, President Johnson was seeking a second full term. He was opposed by Bobby Kennedy in the Democratic primaries.
Johnson could barely appear in public, the anti-war and anti-Johnson demonstrations became so violent. Not only the Left Wing, but also the Right Wing, who felt he was mishandling the war. He finally withdrew himself from consideration.
Bobby Kennedy was assassinated, and Vice President Hubeert Humphrey became the Democratic Party Presidential nominee. At the Democratic convention in Chicago, which was marked with terrible riots in the streets, along with what was termed a "police riot" in response seen on national TV, Democratic chances were sunk. Republican Richard Nixon became President.
Could the same thing happen to a Republican candidate this year? We shall see...