The Biden Backrub is where you politely miss your money shot, purposely aiming with the intention of hitting her shoulders. Then you quickly turn her around and begin massaging the cum around on her shoulders. After this you should be able to sniff her neck to inspect how liberal your cum is.
Liberal version: "Hey Babe, that Pro-Choice Pride rally sure was stressful, I can give you a Biden Backrub if you want?"
Republican version: "Damn, storming the capital sure was a lot of work. I could use a Biden backrub right about now."