Khizr Khan, the Gold Star father who addressed the Democratic National Convention last year, criticized President Trump in a new interview for lacking the "capacity to understand what it takes to serve this nation in harm's way."

In an interview with NPR set to air Monday, Khan was asked to address Trump's conversation with Myeshia Johnson, whose husband, Army Sgt. La David Johnson, was one of four U.S. Army soldiers killed in Niger earlier this month.

"He does not have the capacity to understand what it takes to serve this nation in harm's way," Khan said. "[Trump] is their commander in chief, these are his sons and daughters. How dare he disrespect, how dare he utters a word of disrespect, indignity."

Though Johnson hasn't spoken to the media about her phone call with Trump, Rep. Frederica Wilson, D-Fla., recounted it to numerous news outlets in interviews this week. According to Wilson, who heard the call, Trump told Johnson her husband "knew what he signed up for … but when it happens, it hurts anyway."

Khan told NPR "everything" was wrong with the president's conversation with Johnson.

"Every word is wrong," he said. "These men and women, my sons and daughters, signed up for something more than this president can comprehend. This is beyond his comprehension, patriotism, sacrifice."

Khan appeared at the Democratic National Convention in July 2016 with his wife, Ghazala Khan, to deliver a scathing rebuke of Trump. The couple's son, U.S. Army Capt. Humayun Khan, was killed in Iraq in 2004.

In addition to criticizing Trump's phone call with Johnson, Khan said the president should show empathy and support for both the troops who serve, as well as their families.

"Every word that should come out of his mouth should dignify those wonderful brave family members that now have to bear the burden of that sacrifice," he said. "But this nation dignifies them regardless of the behavior of the president. This nation honors them, honors their sacrifice, honors the sacrifice of those four brave men that went to defend our democracy, our liberty. This nation honors them, honors their families. They're the best of this nation."