These marines are in a form of "rest" I've not seen, or know about.

Hands clasped in the front, perhaps this is a presidential rest, seems like an interesting choice, in any regard, for an official address to the nation, very casual standing there in the back. Casual Fascism.

There is a position with a front hand clasp, but that's when the marine is armed and in parade rest.

From what this anon knows, hands are clasped in the back for parade rest.

Brings me to the question.

"How would biden's speech differ if those marines were armed?"