Multnomah County District Attorney Rod Underhill will not seek re-election in 2020, he wrote in an email to staff June 5.

"After much careful thought, consideration and conversations with family and close friends, I have decided not to run for a third term as Multnomah County's District Attorney," Underhill writes. "My current term of office runs through 2020 and it is my plan to retire at that time."

Underhill has worked for the Multnomah County District Attorney's Office for more than 30 years. His predecessor, Mike Schrunk, served as DA for more than three decades, but the job has gotten more difficult and politically challenging in recent years.

The topic of DA elections has been fraught since a national criminal justice reform movement has gained momentum in recent years. A spate of reform candidates unseated longtime top prosecutors in places like Chicago, Philadelphia and St. Louis, Missouri.

The American Civil Liberties Union of Oregon launched a campaign to educate voters about the power of district attorneys in 2017. The move was seen by some prosecutors as an attack. Just-defeated Bob McCulloch, the St. Louis prosecutor who declined to indict the officer who shot and killed Michael Brown, railed against the ACLU at a conference for Oregon prosecutors last year.

But Underhill has often taken a progressive approach within his office. He de-felonized drug possession charges in Multnomah County before a state-wide law change took effect. And he has been an advocate for alternatives to prison time for low-level offenders.

The decision to retire opens up the field for a contested race to decide his successor.