NASHVILLE (AP) — Conservative activist Andy Ogles announced Thursday he will run for the U.S. Senate seat held by Tennessee Republican Bob Corker, who has so far refused to divulge whether he will seek a third term.

Ogles headed the state chapter of Americans for Prosperity, the political arm of billionaire brothers Charles and David Koch's network that has often displayed a willingness to take on Republicans — including President Donald Trump — when their policies aren't deemed conservative enough. The group announced plans in June to spend up to $400 million in the 2018 midterm elections.

"Over the past several months it has become increasingly clear that too many of our elected officials in Washington are failing our country, failing to fulfill their promises, and failing our future," Ogles said in a release announcing his candidacy.

The Koch network has aggressively pushed to repeal former President Barack Obama's health care law in Congress, and Ogles helped lead successful efforts to torpedo Republican Gov. Bill Haslam's efforts to expand Medicaid in Tennessee.

Ogles also pushed for a repeal of the state's tax on earnings from stocks and bonds that is in the process of being phased out, but he fell short in his efforts this year to defeat Haslam's road funding package that included the state's first gas tax hike since 1989.

"Republican majorities in the House and Senate have not been able to repeal and replace Obamacare, balance the budget, or cut taxes," Ogles said in the release that did not specifically refer to Corker.

"Congress now appears more focused on providing amnesty to illegals to placate so-called Dreamers while refusing to build the wall and secure the American Dream for American citizens," he said.

While several Republicans have expressed interest in running, Ogles is the first to make his bid official. Others considering entering the fray include state Sen. Mark Green, who dropped out of the Tennessee governor's race after withdrawing as Trump's nominee for Army secretary, and former state Rep. Joe Carr.

Ogles, 46, worked on Newt Gingrich's presidential campaign in 2012 before becoming head of the state chapter of Americans for Prosperity in 2013. He has stepped down from the organization to pursue his Senate bid.

Corker told reporters in Washington on Thursday that he will announce his decision about whether he will run again "very soon," saying he had a responsibility to constituents, potential candidates and his colleagues in Congress to let his plans be known.

No incumbent should be surprised to face challengers from within the party, Corker said, citing "the frustrations that people share — that I share" in the current political environment.

Corker, 65, chairs the influential Foreign Relations Committee and his name surfaced as a possible secretary of state in the Trump administration, a job that went to Rex Tillerson. Corker, a former Chattanooga mayor, has $7.5 million cash on hand in his campaign account, according to Todd Womack, a senior aide to the senator.

Corker raised eyebrows last month when he questioned whether Trump had the "stability" and "competence" to become a successful president after comments he made following a violent white nationalist rally in Charlottesville, Virginia.

"Strange statement by Bob Corker considering that he is constantly asking me whether or not he should run again in '18," Trump responded on Twitter. "Tennessee not happy!"

Corker downplayed any rift between himself and the president on Thursday, saying that he has been in regular contact with senior White House officials and that he has a one-one-one meeting with Trump scheduled for Friday.

"Look, I'm blunt person, I grew up in the rough and tumble world of building buildings all around the country, and I speak very frankly," Corker said. "The president does, too, and that's just kind of the relationship we have.

"For people to try to act as if there is daylight between us as a result is just not true," he said.