The U.S. senator from Vermont said Arpaio’s arrests of undocumented immigrants, often separating families, were “outrageous and unconscionable.”

“It’s easy for bullies like Sheriff Arpaio to pick on people who have no power,” Sanders said. “If I am elected president — the president of the United States does have power. So watch out, Joe.”

The crowd of about 900 erupted in cheers. Another 1,900 people who couldn’t fit in the ballroom at the Twin Arrows Navajo Casino Resort near Flagstaff listened to Sanders address them from outside the venue. The crowds were estimated by resort officials.