Former U.N. Ambassador John Bolton said Thursday he's thinking about running for president.

Bolton, a sometimes controversial diplomat who served as ambassador to the U.N. from August 2005 through December 2006 for then-President George W. Bush, flirted with the idea of challenging President Obama in 2012.

"I am thinking about it because I think legitimate issues of national security should be more at the center of the national debate than they have been for the last two years," Bolton said on "Varney and Co." on the Fox Business Network.

Bolton's admission is more blunt than his most recent comments about a potential White House bid. He told the conservative Daily Caller that he wouldn't rule it out, but used the type of language characteristic of many possible candidates, saying he's "flattered" to be mentioned.

If Bolton were to run, he'd enter a potentially crowded GOP field that would square off against each other for the right to face Obama in 2012. While many of those Republican candidates have made the economy the cornerstone of their rhetoric against Obama, Bolton would likely play up his experience on diplomatic and security issues as a cudgel against the president.