Shin, 78, said he has been diagnosed with Alzheimer's disease.
"It is with the deepest regret that I resign from the Senate," said Shin, a Democrat, in a written statement. "I have loved this place and the work we do here on behalf of the people of Washington. Unfortunately, I have determined with the assistance of my family that recent health problems and a diagnosis of Alzheimer's disease make it impossible for me to represent my constituents in the manner they deserve."
In the statement, Shin's family asked for privacy.
Shin's term was to expire at the end of 2014. He announced last year that he would not run for a fifth term.
State Rep. Marko Liias, D-Mukilteo, serves in Shin's district, the 21st. Liias said in the fall that he would seek the Senate seat.
Now he'll seek the appointment to the spot to fill out the remainder of Shin's term -- sooner than he expected, he said.
The last time the two spoke, a few weeks ago, Shin said he still planned to finish his term, Liias said.
"I wasn't prepared for this," Liias said. "I certainly respect that he's got to do what's best for him and his family."
The Snohomish County Democratic party will recommend a name to the County Council to fill Shin's spot, and Liias's spot as well, assuming he is named to the Senate.
"Most likely he'll receive the appointment," county Democratic party chairman Richard Wright said of Liias. "I don't see a (county party) vote that doesn't result in him being the top vote getter." The other representative in the 21st District is Mary Helen Roberts, D-Edmonds.
The 21st District covers Mukilteo, most of Edmonds, unincorporated areas north of Edmonds and Lynnwood and part of south Everett.
Precinct committee officers in the district will meet to come up with three nominees. Then precinct committee officers from around the county will vote on the three names and send the results to the County Council.
The County Council must choose from the three but is not bound to appoint the top vote-getter, Wright said.
Lillian Ortiz-Self, Darrell Chapman and Richard McManus have registered with the state Public Disclosure Commission as 21st District Democratic candidates for the election later this year. Jeffrey Thorp has registered on the Republican side.
The 2014 legislative session begins Monday. Democrats hold a slim majority in the Senate but lost much of their power last year with the formation of the Majority Coalition Caucus, in which two Democratic senators teamed with the GOP to steer policy.
County Democrats have scheduled a meeting for Jan. 18. The earliest an appointment could be made would be the following week, Wright said, well after the beginning of the session.
"We're talking about a body that for either party is critical that they have all their members down there," he said. "We're going to be pressed to do this as quickly as possible."
Shin, Wright said, "has been an extremely effective and well respected senator in the 21st District. He's drawn support and bipartisan respect."
Shin was a street orphan during the Korean War and was adopted by Ray Paull, a U.S. Army officer.
Shin received a GED and eventually a doctorate from the University of Washington and taught for 31 years in Washington's higher education system, according to a statement from the state Senate.
Shin served in the Legislature in 1993-94, ran unsuccessfully for Congress, then was elected to the state Senate in 1998.
During his time there, Shin was known as an advocate for higher education, the developmentally disabled, immigrants, and trade and economic development.
Liias, 32, served on the Mukilteo City Council for two years before he was appointed to the Legislature in 2008.
Shin, he said, "has been a mentor and friend since the days I was on the City Council. He's been a powerful voice on the issues we cared about."
In his statement, Shin thanked his colleagues, family and constituents.
"Most of all, I would like to express my thanks to the citizens of the 21st Legislative District, who placed their trust in my stewardship for all of these years; it has been my honor and privilege to serve them for the past 17 years. I look forward to assisting the Senate in making this transition as smooth as possible."
Bill Sheets: 425-339-3439; firstname.lastname@example.org.
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