As Donald Trump's campaign continues this week embroiled in a series of controversies, a retired four-star admiral, John B. Nathman, has added his voice to the chorus of military voices blasting the Republican nominee over his incendiary comments about the Khan family.

"As Mr. Khan reminded us, it's time now for American leadership to repudiate Donald Trump," Nathman said in a statement. "What is required is not just the recognition of Trump's lack of temperament to serve, but I would add it also takes personal courage to say it out loud."

Nathman is a retired United States Navy admiral who has spoken out in favor of Democratic causes before. He was a co-chairman for then-Sen. Obama's presidential campaign in 2008 and spoke at the 2012 Democratic National Convention. At that convention, the DNC apologized after his speech for accidentally featuring Russian warships behind Nathman during a veterans tribute.

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He has, however, largely stayed out of the political arena in the 2016 election cycle. Nathman's rebuke included a plea to Republican leaders.

"Where is the personal courage of national Republican leaders when it comes to telling Americans this man is not fit for the Presidency of the United States?" Nathman said. "It's time to stop pretending Trump is in any way an acceptable candidate. His unstable temperament and ignorance make it clear he cannot serve as president."

Trump has, in no way, backed down from his handling of the Khan controversy. On Tuesday, Trump repeatedly said he had been "viciously attacked" by Khizr Khan and implied that he was right about his assertion that Ghazala Khan was silent on stage during the speech at the Democratic National Convention because of her Muslim faith. He also said that he had "no regrets" for the way he had handled the family.

The backlash has been swift and bipartisan. Top Republican leaders, including House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, issued statements rebuking Trump (although mostly without naming Trump and without rescinding their endorsements of his candidacy.)