Sen. John McCain thanked well-wishers for their support upon hearing he had been diagnosed with brain cancer, saying he would be back “soon.”

McCain, who had undergone surgery to remove a blood clot at the Mayo Clinic Hospital in Phoenix and was later found to have brain cancer, tweeted “I greatly appreciate the outpouring of support.”

“Unfortunately for my sparring partners, I’ll be back soon,” the 80-year-old senator said. “Standby.”

I greatly appreciate the outpouring of support – unfortunately for my sparring partners in Congress, I’ll be back soon, so stand-by!

— John McCain (@SenJohnMcCain) July 20, 2017

Numerous elected officials and political figures, including former President Barack Obama and former Secretary of State John Kerry, who like McCain served in Vietnam.

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Kerry called McCain “unbeatable, unbreakable” and compared him to President Theodore Roosevelt’s speech about the “Man in the Arena.”

I love @SenJohnMcCain. Unbeatable, unbreakable. He’s Teddy Roosevelt’s “man in the arena” even when we’re on opposite sides. God bless. pic.twitter.com/0sBY4QynWp

— John Kerry (@JohnKerry) July 20, 2017

One of his former sparring partners, former Democratic Sen. John Dingell of Michigan, touted McCain’s toughness.

Jokes aside, I wish my friend @SenJohnMcCain a speedy recovery. He’s tougher than a $2 steak & will be back soon.

Take your time, Maverick. — John Dingell (@JohnDingell) July 18, 2017