While I don't know that humor is the correct response, it is hard to be compassionate when politicians do things that can only inspire anger. To wit, the DNC nominating a candidate for President that clearly should not have been running for any public office, much less the highest in the land. And Biden went along with it. That's far more damaging to the country than poking fun at the president. Biden had the option to retire with dignity. He chose not to. This "decline" didn't start yesterday.
An old man suffering the horrors of dementia certainly deserves compassion. That does not mean that criticism is not deserved as well. Given that Biden has publicly stated that he plans to run for re-election, criticism is all the more deserved.