Republican Senator Bob Corker will not seek re-election next year

WASHINGTON, Sept 26 (Reuters) - U.S. Senator Bob Corker, the influential Republican chairman of the Senate Foreign Relations Committee, said on Tuesday he will not run for re-election for a third Senate term next year.

"After much thought, consideration and family discussion over the past year, Elizabeth and I have decided that I will leave the United States Senate when my term expires at the end of 2018," Corker, 65, said in a statement.

His future had been up in the air for weeks. A former mayor of Chattanooga, Tennessee, and a businessman, Corker had said when he was elected that he could not imagine serving more than two terms in the Senate. He said early this month he had not decided whether he would run.

Corker has been an adviser to President Donald Trump and was on the short list last year to be both his vice president and Secretary of State.

But he has also clashed with the White House.

In August, after Trump's much-criticized reaction to violence at a white supremacist rally in Virginia, Corker told reporters in his home state Tennessee that Trump had not been able to demonstrate the "stability" or competence that he needed to be successful as president.

Trump struck back on Twitter, where he said Corker's statements were "strange" considering that he is "constantly asking me whether or not he should run again in ’18."

"Tennessee not happy!" Trump tweeted.

After the exchange, the two men had an hour-long meeting at the White House this month thatCorker described as a wide-ranging and friendly discussion.

RELATED: Most and least popular senators: July 2017

It was not immediately clear who would succeed him as foreign relations chairman. Jim Risch is the next Republican in line, but Marco Rubio, one of Trump's rivals last year for the presidential nomination, is also a contender.

A fiscal conservative, Corker is known for working with Democrats on a range of issues, from foreign relations to immigration.

His statement alluded to his desire to continue to work "as thoughtfully and independently" in the next 15 months as he has so far in his Senate career.

He has faced some criticism from the far-right, but Corker had $7.5 million in his campaign war chest this month and had been expected to win easily in solidly Republican Tennessee if he had run.

(Reporting by Patricia Zengerle and Susan Cornwell; Writing by Eric Beech; Editing by Eric Walsh and Grant McCool)