Khizr and Ghazala Khan appeared at the Democratic National Convention Thursday in Philadelpha. Their son, Army Captain Humayun S. M. Khan, was killed in combat 12 years ago.

The commander of the Veterans of Foreign Wars says Donald Trump’s criticism of the parents of an Army captain killed in Iraq is unacceptable.

Brian Duffy, head of the 1.7-million-member VFW, said in a statement Monday that election year or not, the nation’s oldest and largest war veterans group will not tolerate anyone berating a Gold Star family member for exercising their free speech. Gold Star families are those that have lost a close relative in military service.

Said Duffy: ‘‘There are certain sacrosanct subjects that no amount of wordsmithing can repair once crossed.’’

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Duffy, who was elected July 27 as the national commander of the VFW, said giving one’s life to the nation is the greatest sacrifice, followed closely by all Gold Star families who have a right to make their voices heard.

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Without mentioning Donald Trump by name, President Obama called on Americans to honor Gold Star families at an event in Atlanta.

“No one, no one, has given more for our freedom and our security than our Gold Star families,” he said. “Our Gold Star families have made a sacrifice that most of us cannot even begin to imagine. They represent the very best of our country.”