I beg, implore, and beseach you to not use our dear president as a model for any type of grammar (or pronunciation, or idiology, or ... really, just don't use him as an example of anything).
Here is an ascending list of force.
She tapped at the door. (Picture finger tips, perhaps for a bedroom door, perhaps to not wake the person inside if they are sleeping.)
She knocked on the door. (Normal - you use the back of your knuckle.)
She rapped at the door. (Not very different from knocking, but perhaps a bit more forceful.)
She banged on the door. (I'd assume a closed fist, using the side where your litte finger is.)
She beat on the door. (This might be two fists, used as above.)