The difference is that a president's approval rating can rise without a catastrophic event, but their approval will only likely fall in the event of bad news for America.
This is disingenuous.
Basically, your argument amounts to the old tired sophistry that any criticism of x (in particular where x = the President) is unpatriotic. Such an argument is fallacious, insulting, offensive, and runs counter to the ideals we ought to hold true in a free and open democratic society.
And yes, while I suspect that using this sort of argument is/was less prevalent by Democrats under Obama than it was/is among Republicans under Trump and Bush, this is also the case when some Democrats/liberals made the same argument about Obama (I certainly never made any such argument).
You should be able to distinguish between disagreeing with or disapproving of a person, the way that person conducts themselves, and that person's policies and wanting bad things to happen to America.