Military chiefs have concerns about the politicization of President Donald Trump’s July 4 event, a source with direct knowledge told CNN.

In the planning for the event, they had reservations about putting tanks or other armored vehicles on display, the source said.

As the final details come together, several top military chiefs of the individual services are not attending and are sending alternates in their place, though some say they had prior plans. The Chairman of the Joint Chiefs, Marine Corps Gen. Joseph Dunford, will attend.