1 rain drop,
Is the line on his neck changing with the light, or is it constant?
I believe it’s constant.
The reporter also has that line on his right side. It's not as pronounced as biden's and it is lighter on his left side (side away from the strong light).
At the 0:50 mark, one can see biden's jacket is too high up his head. He's wearing a zip up sweater under his jacket. Maybe this is causing a double shadow? one shadow would be constant because of it's high resting place on his head?
Then at 4:12, biden pulls back and the color changes by his collar bone to lighter. His shirt collar is pretty high up and this would be the constant shadow.
He has many layers causing shadows.
The bar they're at is pretty dark and they have very strong lights focused on them.