The bottom line is Trump staged a publicity/political event in Section 60 or the Arlington National Cemetery were only cemetery photographers are allowed. When Trump began doing his photoshoot a official with the cemetery tried to stop them and was pushed aside.
This is a statement from Trumps team confirming it...
In a statement to NPR, Steven Cheung, the Trump campaign's spokesman, strongly rejected the notion of a physical altercation, adding: "We are prepared to release footage if such defamatory claims are made.
"The fact is that a private photographer was permitted on the premises and for whatever reason an unnamed individual, clearly suffering from a mental health episode, decided to physically block members of President Trump's team during a very solemn ceremony," Cheung said in the statement.
"Federal law prohibits political campaign or election-related activities within Army National Military Cemeteries, to include photographers, content creators or any other persons attending for purposes, or in direct support of a partisan political candidate's campaign," according to the statement. "Arlington National Cemetery reinforced and widely shared this law and its prohibitions with all participants."