Donald Trump Jr. is using a tragedy to mock the actor who skewered his father on Saturday Night Live. A T-shirt that reads “Guns Don't Kill People, Alec Baldwin Kills People" is selling for $27.99 on a merchandise site linked to the former president's namesake son. The reference is to last week's killing of cinematographer Halyna Hutchins, who was hit by discharge from a prop gun while working on the Baldwin film Rust. Baldwin, the film's star, was handling the weapon from which the fatal shot was fired. The movie's director was injured too. Trump Jr.'s merchandise site also sells shirts t...