He was clearly talking aloud to himself, reflecting on the importance of saluting our marines. He didn't actually salute them this time because he was celebrating a historic day.

edit: I'm being sarcastic, guys. Biden also violated his own executive order on masks, and his press secretary said it was because he was celebrating a historic day. I guess I was too subtle with this one...

He was clearly talking aloud to himself, reflecting on the importance of saluting our marines. He didn't actually salute them this time because he was celebrating a historic day.