WASHINGTON ― Sen. John McCain (R-Ariz.), who lost the 2008 presidential race, sharply criticized Republican presidential nominee Donald Trump on Thursday for not pledging to accept the result of the November election.

McCain said the loser’s obligation to concede was about “respect.”

“I didn’t like the outcome of the 2008 election. But I had a duty to concede, and I did so without reluctance,” McCain said in a statement. “A concession isn’t just an exercise in graciousness. It is an act of respect for the will of the American people, a respect that is every American leader’s first responsibility. Whatever our differences we owe each other that respect, which we express by defending the democratic values and practices that protect us all.”

During Wednesday’s presidential debate, Trump was asked whether he would pledge to accept the election results despite his numerous claims that the system is “rigged” against him.

“I will look at it at the time,” he replied. On Thursday, Trump elaborated, saying he will accept the result ― if he wins.

In every previous election, the loser congratulates the winner and calls them, ‘my president.’ That’s not just the Republican way or the Democratic way. It’s the American way. Sen. John McCain (R-Ariz.)

McCain said accepting the will of the voters is an American tradition.

“I don’t know who’s going to win the presidential election,” McCain said. “I do know that in every previous election, the loser congratulates the winner and calls them, ‘my president.’ That’s not just the Republican way or the Democratic way. It’s the American way.”

Citing no evidence, Trump has repeatedly questioned whether President Barack Obama can legitimately serve as president. He has publicly questioned whether Obama is really a U.S. citizen, called him as “your president” and used air quotes when referring to him as president.

In October 2008, as McCain and Obama were in the final stretch of their campaigns, the Arizona senator also spoke about the importance of accepting the result of the election.

“I’ve come out on both sides of elections. And I’ve never lost my confidence in the judgment of the American people. In the military, they work pretty hard to impress the chain of command on your thinking. And one way or another, on the fourth of November, word will come down from the top of the chain, and Sen. Obama and I will both receive our orders,” he said.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.