The 30-second ad is part of an already-announced buy in Iowa and New Hampshire, the first two states in the Democratic primary.
Gun control has become a top issue in the primary. Clinton has said she supports universal background checks, prohibiting domestic abusers from purchasing guns and repealing legal protections for gun manufacturers, among other measures. She has called for a “national movement” to take on the National Rifle Association.
In the 2008 primary against then-Sen. Barack Obama, however, Clinton took a more moderate tone on gun, emphasizing her “wholehearted support” for the Second Amendment.