Duncan was first elected in a 1988 special election.

He replaced his father, John J. Duncan Sr., who was ill with cancer.

Duncan Sr., had held the seat for 23 years.

Duncan Jr., has been in office for nearly 29 years.

WASHINGTON – Rep. John J. Duncan Jr., the longest-serving Tennessean in Congress, will not seek re-election next year, bringing to a close the career of one of the state’s most enduring officeholders and ending a family political dynasty that has occupied the East Tennessee congressional seat for half a century.

In a statement to the Knoxville News Sentinel, Duncan announced Monday he would would step down from office when his current term ends at the close of 2018.

“It has been a very special privilege to represent the people of the Second District in the U.S. House of Representatives,” the Knoxville Republican said. “However, I will not be running for re-election in 2018.”

Duncan, who turned 70 on July 21, said he had considered retiring even before his last election in 2016.

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“Since then, in part, because people knew or assumed that I might be thinking about retiring, I have never had so many people urging me to run again,” Duncan said. “Also, because of the recent attacks against me from the far left, my support among the conservative Republican base has never been more enthusiastic. I am grateful for their kind expressions of support. However, now is the time for me to move on to the next chapter of my life.”

Duncan’s announcement came just a few hours after Knox County Mayor Tim Burchett said he would disclose his own political plans at an event on Saturday. Burchett is expected to run for Duncan’s seat.

"I am grateful for Congressman Duncan's friendship, and I appreciate the years of service he and his family have dedicated to our community," Burchett said in a statement after hearing about Duncan's retirement announcement.

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"He has been a consistent, conservative voice for the 2nd District, and he's represented us well. Few families have made a bigger impact in East Tennessee than the Duncan family, and I have no doubt they will continue to make a difference."

In an interview after Duncan's announcement, Burchett declined to say whether he intends to run for Duncan’s seat.

“I’ll still be making my announcement on Saturday,” he said. “I think it’s time we reflected on Congressman Duncan and his family’s service to our community.”

Read more:

Knox County Mayor Tim Burchett to announce campaign plans Saturday

Duncan, a social and fiscal conservative who often broke rank with his fellow Republicans, was first elected to Congress in a special election in 1988 to replace his father, John J. Duncan Sr., who was ill with cancer.

Duncan Sr., who had been the mayor of Knoxville, held the congressional seat for 23 years. Duncan Jr. surpassed his father’s record of service in April 2012 and has now held the same office for nearly 29 years.

'I love my job, but I love my family more.'

In his statement, Duncan stressed that after more than a quarter-century in the job, he felt the time had come to move on.

"I have decided I wanted to spend less time in airports, airplanes, and traveling around the district and more time with my family, especially my nine grandchildren, who all live in Knoxville,” he said. “I love my job, but I love my family more.”

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While in Congress, “I’ve worked as hard as I can to fight for what I believe in – fiscal conservatism, smaller government, and a more humble foreign policy that puts America first,” he said. “The most rewarding part of the job though has been being able to help many thousands of people on a personal level.”

Duncan thanked the people of East Tennessee “for giving me the privilege to serve for what will be slightly over 30 years in Congress at the end of this term.”

“My family has sacrificed much to allow me to serve, and I especially thank my wife, Lynn, and my four children, all of whom have greatly helped me during my time in Congress,” he said. “I also want to thank my excellent staff, especially Bob Griffitts and Jenny Stansberry, both of whom have been with me the entire time I have been in this position."

Tennessee’s 2nd District is the 28th most Republican District in the country, according to the Partisan Voter Index calculated by the Cook Political Report. The index measures how each district performs at the presidential level compared to the nation as a whole. Republican Donald Trump defeated Democrat Hillary Clinton by a 35.4 percentage point margin in the 2016 election.

'Consistent conservative voice'

In an interview, Burchett praised Duncan and his father for their service and said the Duncans have been role models for other officeholders, including himself.

“(The Duncans) been a consistent conservative voice in the region for years,” Burchett said. “We tried to model our office after his constituent services. Nothing can compare to it, the way they deal with folks.”

“Very few families have made a bigger difference than his family has, and he will continue to make a difference — I’m sure of it.”

Burchett also credited Duncan for helping fuel the state’s growth.

“The reason we have (done well as a state) is because we’ve tried to reduce the number of government bureaucrats that stifle that kind of growth, and he’s been on the forefront of that and keeping them in check,” Burchett said. “If the rest of Congress voted like Duncan did fiscally, we’d be out of debt.”

Duncan had independent streak

Though a stalwart fiscal and social conservative, Duncan at times had an independent streak that put him at odds with his own party.

His biggest split with the GOP came in 2002, when he resisted pressure from Republican leaders and top-ranking officials in then-President George W. Bush’s White House and refused to support a resolution authorizing war with Iraq.

Duncan said he felt the Bush administration had failed to show that Iraq posed a serious threat to the United States. He was one of only seven Republicans — six in the House, one in the Senate — to vote against the war and is the only one of those seven still in office.

Just last week, Duncan again made headlines when he became one of only three House members to vote against a bill to toughen sanctions on Russia and make it harder for President Donald Trump to ease the sanctions against Moscow.

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The bill, which punishes Russia for meddling in the U.S. presidential elections and for its military aggression in Ukraine and Syria, also targets Iran and North Korea for their illicit ballistic missile programs and support for terrorism.

Duncan said he was reluctant to impose sanctions on all three countries, adding, “I think we should stop trying to rule the whole world."

A few weeks ago, Duncan came under fire after news reports disclosed that his campaign had paid $293,250 to his son, John J. Duncan III, over the past five years. The payments started just two weeks after Duncan III pleaded guilty to a felony charge of official misconduct tied to his tenure as the Knox County Trustee.

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The congressman defended the payments, saying his son had been in charge of his entire political operation for the past four years and that he had been paid far less than many campaign managers and consultants.

Reporter Tyler Whetstone in Knoxville contributed to this story.