The last book Khizr Khan sent his son Humayun, an Army captain who was killed in a 2004 car bombing in Iraq, was Sen. John McCain’s “Why Courage Matters.”

Khan said he has long respected the Arizona Republican, and that one of his last conversations with his son had been about the book and McCain’s “sacrifice and (the) sacrifice of others to strengthen and care for others.”

McCain had been “my and my family’s hero,” whom Khan said they admired as someone who “gave so much in care of others” both as a veteran and as an elected official.

It’s that admiration that led Khan to call on McCain and other GOP leaders this week to withdraw their support of GOP presidential nominee Donald Trump.

“I implore Sen. McCain … I continue to implore all of the good Republicans who either support or are going to vote for their party’s candidate, this will be a historic moment in the Republican Party,” Khan said Tuesday during an interview with Cronkite News.

“If you publicly rebuked him, you will look back and you will stand tall in front of the nation and you will say you were not for this, we were for (a) better America,” he said.

McCain issued a blistering denunciation last week of Trump’s attacks on Khan and his family, but he has refused to back away from his statement that—without naming Trump—he will support “the party’s nominee.”

McCain’s office did not return calls and emails requesting comment on Khan’s statements.

Khan came into the public eye two weeks ago after his speech at the Democratic National Convention in Philadelphia, where he assailed Trump for what he calls the nominee’s anti-immigrant and anti-Muslim rhetoric.

In that nationally televised convention speech, Khan held up one of the pocket-sized Constitutions he hands out to guests to his home and asked Trump whether or not he had read it. Khan, a Muslim immigrant from Pakistan, then went on to say that Trump had “sacrificed nothing and no one” for the country.

Trump fired back, saying that he had made many sacrifices for the country by working hard and creating jobs. He went on to say that Khan seemed like a “nice guy,” but suggested his speech was written by Democratic nominee Hillary Clinton’s campaign and wondered if Khan’s wife Ghazala, who stood quietly next to him during his DNC speech, was not “allowed to have anything to say.”

Trump’s campaign did not return an email asking for comment Tuesday.

But his sniping at a Gold Star family was jumped on by Democrats and almost as quickly criticized by veterans’ groups and by Republican leaders, including McCain, House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell.

In a statement from his campaign, McCain blasted Trump’s attacks on the Khans, saying the comments “do not represent the views of our Republican Party, its officers, or candidates.”

“In recent days, Donald Trump disparaged a fallen soldier’s parents,” McCain said in his Aug. 1 statement. “He has suggested that the likes of their son should not be allowed in the United States – to say nothing of entering its service. I cannot emphasize enough how deeply I disagree with Mr. Trump’s statement.”

McCain went on to thank the Khans for immigrating to the U.S. when Humayun was 2, and to say that their son “was the best of America.”

While he has never endorsed Trump by name, McCain has said repeatedly that he will support the Republican nominee – which, as of three weeks ago, is Trump.

Trump made waves in the party last week when he said he was “not ready” to endorse McCain, House Speaker Paul Ryan and other leading Republicans who have not embraced his candidacy, although he relented and endorsed them over the weekend.

Khan said McCain and other GOP leaders need to take their repudiation of Trump and his remarks one step further.

“They don’t want to have that burden on their conscience,” Khan said. “That was the time to speak. This is the time to stand for whatever they want to stand.”

Trump supporters, including some Muslim supporters, have criticized Khan, who they said has disrespected his son’s memory by politicizing his death.

But Khan disagrees, saying that his wife and he have paid tribute to Humayun by speaking out for the values their son fought for.

“He would be standing right here, with his left hand on my left shoulder, because that is the connection of my heart with him,” Khan said Tuesday, pointing to the spot next to his chair. “He would be standing there and smiling, ‘Thank you.'”

Despite his opposition to Trump and his displeasure with GOP leaders’ reluctance to take back their support of the nominee, Khan said that this election season has not affected his view of the U.S.

“This is not the perfect place, this is the best place,” Khan said. “And we can make it better.”

Cronkite News reporter Wafa Shahid contributed to this report.