Chris Hayes is joined by Sen. Elizabeth Warren, Gov. Roy Cooper, Minnesota AG Keith Ellison, former Minnesota Sen. Al Franken, Michelle Goldberg, and Heather McGhee to discuss Kamala Harris' pick for vice president: Tim Walz.

Guests: Jamelle Bouie, Meredith McGraw, Fernand Amandi, Margie Omero, Jon Allen, Ben Rhodes

A rambling news conference from a clearly rattled Trump. How the Republican front-runner was caught flat-footed—and what it means for his campaign. Then, what the latest polling says about the Harris-Walz campaign—and the challenges of running while vice-presidenting.