Harper's surprise resignation came moments after the Legislature ended its special session dealing with measures to land the 777X jetliner program in Everett.
"Unfortunately my work in Olympia takes me away from my family far too much," Harper said in an interview Saturday.
"I ran because I believed I could do a better job representing the district," he said. "But to be a full-time husband, to be a full-time father and to maintain my full-time law practice, I cannot continue to give this job the amount of dedication it deserves or the people of the district deserve."
Harper, 34, is married and has two young daughters, both of whom have been born since he took office.
Harper's announcement caught many of his colleagues off guard, because up until a few days ago he had been campaigning to succeed Ed Murray as leader of the Senate Democratic Caucus. Murray left the Senate this week following his election as mayor of Seattle.
"It's a loss. Nick is a really valued member," said Sen. David Frockt, D-Seattle, who is the interim caucus leader. "We wish him and his family the best."
The sudden exit added fuel to rumors of an extramarital affair involving Harper and a lobbyist in Olympia. Harper declined to respond when asked if the allegation was true or if the weight of the rumors played a factor in his decision.
"I am leaving office for the reasons I've just stated. It is unequivocal. I have no regrets. I have no reservations," he said.
The departure derails the career of one of the Democratic Party's brightest hopes and concludes one of the more interesting chapters in Everett political history.
In September, the Washington State Democratic Party named Harper its Male Elected Official of the Year.
He enjoyed wide support from the progressive flank of the Democratic Party and was expected to easily win re-election in 2014. At the same time, he earned broad respect from Republicans in the Legislature.
After three years, most had forgotten that some in the Senate did not want him seated following his victory in 2010.
He was 31 when he unseated an incumbent senator and fellow Democrat, Jean Berkey, in his maiden bid for public office.
He had been strongly recruited by progressive forces who were frustrated with Berkey's moderate leanings. Harper triumphed in an election tainted by the efforts of an independent political committee to help him win.
Moxie Media, the Seattle political consulting firm running that committee, was later slapped with a heavy fine by the state for concealing the source of money that paid for mailers and phone calls attacking Berkey in the final days of the August 2010 primary.
Berkey tried unsuccessfully to get the election results thrown out and a new election held. Some of her friends in the Senate considered trying to block Harper from taking office because of what transpired.
At the time, Harper did not denounce the shenanigans. He would go on to co-sponsor legislation imposing tougher rules on disclosure on the source of money and the membership of independent committees.
Harper is leaving office with a full year left in his term as representative of Everett and Tulalip in the 38th District. He said he was not disappointed about leaving his term unfinished.
"What I've accomplished in three years I am very, very proud of," he said.
Helping Washington State University to establish a foothold at Everett Community College and giving the four-year university a visible presence in the city is the achievement he said he's most pleased with.
The Snohomish County Council will choose Harper's successor from names put forth by the district's Democratic precinct officers. It is expected that person will be chosen in time to serve in the 2014 legislative session.
Reps. Mike Sells of Everett and John McCoy of Tulalip are two of the most prominent names mentioned Saturday as possible candidates.
Jerry Cornfield: 360-352-8623; firstname.lastname@example.org.
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