The first day ended with the defense team announcing that it had subpoenaed U.S. Attorney General Jeff Sessions. The Department of Justice has filed a motion to quash.
In a 16-minute opening statement for the bench trial, federal authorities said Arpaio knew he was ordered to cease enforcing federal immigration law, ignored the order, then bragged to the press about it.
Arpaio's attorney forcefully countered in a 20-minute opener that the sheriff only enforced the law.
Arpaio, in a dark suit, sat stoically throughout the proceedings. Sometimes he rested his chin in his palm. Other times, he leaned forward, listening intently and taking careful notes.
The gallery, mostly filled by supporters and critics of the controversial seven-term sheriff, were rapt by the testimony.
The government has charged Arpaio with criminal contempt of court. If convicted, he could face six months behind bars. The charges stem from the original Melendres vs. Arpaio racial profiling lawsuit.
Prosecutor Victor Salgado made the government's case.
"He wore his defiance for political gain," Salgado said. "He of all people knows that when the court speaks, you listen."
Salgado described the court order by U.S. District Judge Murray Snow as "clear, precise, and definite."
But Dennis Wilenchik, defending Arpaio, said, "You can ram a truck through those words."
"They can dress it up any way they want, but that's not what this case is about," Wilenchik argued.
Wilenchik noted the U.S. Supreme Court ruled in a related civil suit that Arpaio's cooperation with the federal government was "constitutional, absolutely constitutional."
The defense attorney called the case against Arpaio "shameful and outrageous," and said Arpaio was the only one "to get it right."
The trial began with the news of the death of Jack MacIntyre, a key Arpaio associate who took the fall for evidence destroyed in the original civil rights case. Whether MacIntyre's deposition will be allowed was debated.
The morning ended with stop-start testimony from Timothy Casey, Arpaio's attorney in the civil rights lawsuit.
Through dozens of objections, many sustained by a visibly frustrated Judge Susan Bolton, the government established that Casey met repeatedly over two years with Arpaio and advised him about the injunction.
Wilenchik argued that Casey "dropped the ball and threw the sheriff under the bus," adding that such conversations never existed.
Casey's testimony continues this afternoon.