There is a lot of speculation about Biden's approach to the first presidential debate tonight -- will he ramble off-topic? Lose his his temper? Let Don get away with lies? There isn't much speculation and Don's approach -- reports indicate he'll repeat what he did against Hillary Clinton.
It's useful to remember that what gets under Don's skin is not being seriously challenged, but being not taken seriously. At heart (I speak figuratively), he is an eight-year-old bully who hates to be laughed at instead of feared. It might be useful to consider one of the best examples of this: The 2011 Correspondents Dinner, where President Barack Obama made his face turn orange. To this day, his face is still orange.