U.S. Sen. Angus King is endorsing Vice President Kamala Harris for president, King announced on his Instagram page on Thursday.

“For the first time in my life, I know a presidential candidate personally, and I got to know Kamala Harris in a unique way,” King wrote.

King, an independent who is seeking a third term in the Senate and faces three opponents, wrote in the post that he got to know Harris through the four years they spent together on the Senate Intelligence Committee.

He said many of those meetings were closed to the public because they contained classified information. That’s when saw Harris ask tough questions and described her as “quick and whip-smart, she is steady and calm under stress.”

“She is passionate about two things — the truth and our democracy,” King wrote. “These are the qualities I want in a President, and this is why I’m voting for Kamala Harris.”

King, who caucuses with Democrats, is facing Republican Demi Kouzounas, Democrat David Costello and independent Jason Cherry on the Nov. 5 ballot.

King is the second member of Maine’s congressional delegation to endorse Harris, following U.S. Rep. Chellie Pingree (D-1st District). U.S. Rep. Jared Golden (D-2nd District) has said he will not endorse any presidential candidate and Sen. Susan Collins, a Republican, has said she will write-in former Republican nominee Nikki Haley.