Barbara Starr is CNN's Pentagon correspondent. The views expressed in this commentary are her own. View more opinion articles on CNN.

(CNN) The 1.3 million members of the US military have one thing in common. Each one has taken an oath to defend the Constitution of the United States. They have sworn that they are willing to die in combat to defend the core values of this country. And that means they are willing to die on the battlefield for freedom of speech and freedom of the press.

Continuing to attack both of those fundamental American pillars is clearly something that President Donald Trump feels resonates with his political base, even after 19 months in office. But as the Commander in Chief continues uninterrupted in his attacks, there is a problem boiling to the surface. Defense Secretary James Mattis and Chairman of the Joint Chiefs General Joseph Dunford -- two of the top commanders -- are walking an increasingly fraught line, ordering troops to fight and die under a Commander in Chief who does not publicly share the values the troops are obligated to defend.

Trump is now an accelerant. At what was supposed to be a presidential speech to the Veterans of Foreign Wars this week, the President, as he almost always does, attacked the media, saying , "Don't believe the crap you see from these people -- the fake news." Many in the audience cheered. And Dunford had just been there the day before. The VFW scolded its members on their reaction to Trump, saying it relies on the media to cover veteran's issues.

But there had been a little noticed, more worrisome incident. In March, Trump appeared at the Marine Corps Air Station Miramar near San Diego. Speaking before hundreds of Marines, he again pointed to reporters covering the speech and called them "fake news," leading hundreds of uniformed personnel to applaud wildly for a political statement attacking a press corps they are sworn to defend.

Military personnel are banned from political statements and activities. The United States military is the strongest in the world -- not because of its billions of dollars in weapons -- but because it serves the interests of the American people, instead of American political agendas. Senior Marine Corps leaders watched the Miramar event aghast, but did nothing.

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