WASHINGTON (AP) — Sen. John Kerry, the next secretary of state?

Republican Sen. John McCain had some fun Monday at the expense of his friend and Democratic colleague. Responding to a Kerry introduction at a news conference on a disabilities treaty, McCain said, “thank you very much, Mr. Secretary.”

It was a clear reference to the recent talk that Kerry is a top candidate to replace Secretary of State Hillary Rodham Clinton. It was also a nod to McCain’s opposition to the current front-runner, U.N. Ambassador Susan Rice.

Kerry gave it back with his own quip, one that pained McCain.

“Thank you very much Mr. President,” Kerry said when he returned to the microphone. McCain unsuccessfully sought the presidency in 2000 and 2008.