With a law degree under his belt, the career-conscious Lt. Daniels was once on the fast track to becoming a major, and after that, quite possibly a colonel, deputy commissioner or higher. But all that changed when McNulty compelled Judge Phelan to take an interest in the Barksdales. The bosses tapped Daniels to lead a fast, straightforward - and above all, limited - investigation. Daniels understood his charge, but faced with the realities of what was required to pursue the Barksdale case, he found himself drawn inexorably toward a wiretap that his superiors did not want. And when the investigation started to target the money trail, Daniels got behind his unit and jeopardized his career by defying Commissioner Burrell's order to shut it down.
This strained his marriage to his politically ambitious and well-connected wife, Marla, who feared that everything they'd worked and waited for was on the line - especially after Burrell threatened to reveal a long-buried corruption scandal that occurred during the lieutenant's early days in Eastern District. Daniels ignored the threat and brought in the Barksdale case, though Burrell exacted his revenge in the end - assigning Daniels to clerk duty in the evidence room.
That turned out to be short-lived, as another case soon required his attention: Major Valchek's petulant feud with dockworkers' union boss Frank Sobotka over a window donated to a Roman Catholic church in the city's Polish neighborhood. Valchek demanded that Daniels lead his anti-corruption probe of the dockworkers local on the basis of his son-in-law's recommendation. Happy to be out of the evidence room, Daniels agreed. But the probe became meaningful when it tied into drug smuggling, human trafficking and murder. After bringing in some arrests on that second case, Daniels was given a permanent wiretap detail, and set his sights on the Barksdale organization once again. This time, the unit made good on years of police work. Despite constant setbacks, Daniels finally made the rank of major, and did it his own way.
But it wasn't fast enough for his wife, and the marriage broke apart. For a time, Daniels pretended otherwise to allow Marla to better run for city council with her husband on her arm. But eventually, Daniels found a new romance with A.S.A. Rhonda Pearlman, and with Mayor Thomas "Tommy" Carcetti now backing Daniels' ascent through the department, the pair appear on the verge of becoming a power couple.