Editor’s Note: 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.

Trump has now taken it a step further with what some say is an Orwellian declaration: “What you’re seeing and what you’re reading is not what’s happening.” But troops don’t have the luxury of serving only the parts of the nation’s fabric they agree with. They serve the nation. Despite Trump’s tendency to talk about the military as “his’” and “my generals,” nothing could be further from the truth. The US military is and must stay apolitical. It is not Trump’s.

So how long can Mattis and Dunford remain silent? Their own aides privately acknowledge both are in a tough position. They cannot contradict the President publicly. But outright politicization of the military is exactly what Dunford privately feared all the way back to the presidential campaign. He regularly declines to publicly answer any questions he feels touch too closely on Trump’s political agenda.

Mattis has gone further. He does not do interviews, and he has only appeared in front of the Pentagon briefing room cameras a handful of times. His own aides readily admit he becomes furious at stories or questions that appear to address any disagreements between him and the President, concerned a rift will sideline his influence with the President.

But many feel it’s all gone too far. Americans have a right to know the state of the US military. To keep a military low profile, Mattis had clamped down on releasing basic military information that has been publicly available for years. For example, the Pentagon no longer publishes a regular report on troop levels in Iraq, Syria or Afghanistan. Mattis believes it gives adversaries valuable information, even though there is no way of knowing how many are at any one location on a given day. Over time the Pentagon has provided what it describes as approximate numbers for Iraq, Syria and Afghanistan. Mattis has also forbidden detailed discussion of military “readiness,” whether the troops have all the training and equipment to fight.

However, as one military officer put it to me, “How much longer can he hide?” Mattis has not yet commented in detail on Trump’s Helsinki meeting with Vladimir Putin – even as he, as secretary, has taken a publicly hard line on Russia. He also has not commented on Trump’s latest threats against Iran, even as Iran has threatened to shut down Gulf oil shipping.

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    Everyone who knows Dunford and Mattis says they would never resign unless they are ordered to do something illegal, unethical or immoral – an unlikely scenario by all accounts. But the US military may be facing more significant dangers right now: Leaders who stay quiet, information that is not communicated to the public and young troops who don’t know they can only serve effectively by not engaging in fleeting political agendas.

    When a casket of a returning fallen servicemember is met at Dover, nobody knows if they are a Republican or Democrat. What we know is they are American heroes. Senior leaders know they must keep that legacy alive for the generations who served before and those still to come. The challenge for today’s military leaders will be knowing when it is time to stand up and speak their minds in defense of the American values that the military has sworn to uphold.

    Clarification: This article has been clarified to note that the Pentagon has provided approximate troop levels in Iraq, Syria and Afghanistan.