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Graves and his spokeswoman did not immediately to questions about the timing of his announcement and future plans.
It appeared to take many of his colleagues by surprise. U.S. Rep. Doug Collins issued a statement Thursday afternoon saying Graves’ absence will leave a void.
“Tom’s decision not to seek re-election leaves a major hole in the Georgia delegation,” Collins, a Gainesville Republican, said. “Throughout his time in Congress, Tom has been a prime example of the power of hard work and leadership."
Isakson, who is retiring at the end of the year and whose seat Loeffler will fill, said he was sorry to hear Graves would be stepping down.
“His rise in the U.S. House reflects his leadership and his commitment to serving others,” Isakson’s statement said. “He is one of a kind – a great Georgian, a great American and a great representative of our state.”
State Democrats cheered Graves’ decision, casting it as an acknowledgement by Graves that President Donald Trump’s administration and agenda were in trouble in 2020.
“Tom Graves is quitting Congress because he knows the same thing we do: Republicans’ time is running out,” said Scott Hogan, the executive director of the Democratic Party of Georgia.
Avery Jaffe of the Democratic Congressional Campaign Committee issued a reminder that “Republicans in safe seats don’t usually retire if they think their party is going to win back the majority in Congress next year.”
The governor, meanwhile, called him a strong conservative who was committed to “championing the values and principles that make our state and nation great.”
First elected to Congress in 2010, Graves had transformed himself from a sharp-edged bomb-thrower into a more pragmatic lawmaker over the years. That rebirth helped him amass power on Capitol Hill, but also alienated some conservatives.
A real estate investor who grew up outside of Cartersville, Graves was elected to the Georgia House at age 32, but quickly fell out of line with powerful Republican leaders.
He created the 216 Policy Group of independent conservatives that often infuriated then-House Speaker Glenn Richardson and his top allies, and then eventually aligned himself with the then-fledgling tea party movement.
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That alliance helped bolster his 2010 bid to win a scarlet-red U.S. House district in northwest Georgia.
He’s scored overwhelming victories ever since, winning another term last year with roughly 77% of the vote by defeating a little-known Democrat who ran his campaign from a jail cell.
Once elected, Graves earned national attention as the House Republican leading the anti-Obamacare charge that led to the 2013 government shutdown.
In recent years, he’s charted a more pragmatic course, amassing influence that made him one of the most powerful Georgians in the U.S. Capitol.
However, there were setbacks along the way.
Graves unsuccessfully ran for chairman of the Republican Study Committee, an influential group of conservative lawmakers, losing to U.S. Rep. Steve Scalise in 2012. And he also lost a race to become the top-ranking Republican on the House Appropriations Committee.
As a consolation, he became the ranking GOP member on the House's modernization committee and was the only Georgia member appointed to a special committee created to figure out funding for President Donald Trump's border wall.
Long seen as a potential statewide candidate, Graves surprised insiders by not submitting his application for the open Senate seat that was filled Wednesday by Loeffler's appointment.
Graves becomes the second Georgia Republican to announce he won’t seek another term in the House after U.S. Rep. Rob Woodall, who said he was retiring shortly after winning the nation’s tightest U.S. House race in 2018.
Among the possible Republican contenders for the seat are Paulding County school board member Jason Anavitarte, state Reps. Steve Tarvin and Katie Dempsey, House Majority Whip Trey Kelley and state Sen. Jeff Mullis.
Staff writer Greg Bluestein contributed to this report.