U.S. Sen. John McCain, the 2008 Republican presidential nominee, said he will run for his sixth term in 2016.
The Arizona Republican, 78, made the announcement Monday in an interview with NBC News. He will be 80 by Election Day, but he said his Senate career is "just getting started."
Tea party groups see him as a top challenge in the primary, and conservatives have criticized him as too liberal.
To win, McCain said he will emphasize issues in Arizona, such as the drought, his work to benefit a copper mine and legislation to reform the Department of Veterans Affairs.
The VA was thrown into turmoil last year amid allegations of misconduct and cover-ups at the VA hospital in Phoenix. Investigators say veterans' health was jeopardized when employees covered up long wait times for patients.
Meanwhile, McCain uses his position as chairman of the Senate Armed Services Committee to criticize the national security policies of President Obama, whom he lost to in the 2008 election.
"I have never been more concerned about the security of this nation because of the feckless leadership of the president of the United States," he said.