I think the Dems use of “pounce” was first restricted to the particular situation where the Dems have taken a course of action that the Pubs warn will end in a bad result, but the Dems dismiss the warning, then when the inevitable bad result happens, just as predicted, and the Pubs say “I told you so”, the Dems try to excuse their incompetence by claiming the Pubs are “pouncing’.
Yes, the word “pounce” implies an unfair sneak or blitz attack that’s unethical and illegitimate. That’s why it’s never used to describe attacks from the Democrats.