CHICAGO — Sen. Ruben Gallego, D-Ariz., gazed at the Chicago Hilton Hotel’s vaulted ceilings and reflected on its grandeur. When he was a kid growing up with a single mother on Chicago’s South Side, he said, he couldn’t dream of being in a place like this. Once he entered an expansive ballroom packed with 900 people — a mostly Latino audience attending the Hispanic American Construction Industry Association's annual dinner — Gallego, who can move in and out of speaking Spanish, shook hands and