Tim Walz's Proud Son Cries During Dad's Speech at DNC

Play video content Gov. Tim Walz's big moment at the DNC brought the crowd to its feet, especially his 17-year-old son ... whose emotional reaction to his dad's speech became a real tearjerker moment. Gus Walz sat front and center Wednesday night in Chicago, and he just couldn't hold back his emotions in the moment -- breaking into tears and screaming "That's my dad!" during the speech. Check out the clip ... Gus…