Members of the armed forces are required to salute the President. However, their command's orders about how to present that salute is a matter of command discretion. The Marines who greet the President's helicopter will follow their commands orders.

Lilo, you originally posted that "No previous US President has bowed to the Emperor of Japan." The picture of Nixon meeting Hirohito in Alaska is of Nixon bowing to the Emperor. As I posted above, the President can bow to whomever he wants to bow to and in the way he wants to without impugning anything. This Nation and its Presidents have enough quality and self-esteem to "endure" any attendant criticism. Right TB. It's not earthshattering.

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