In my current game as Brandenburg/Prussia. Bohemia has been PU'd with Mazovia(eastern poland) and more importantly Saxony and the Palatinate. Both electors. I have beaten Bohemia in several wars. AI Austria has also yet I can't make Prestige drop low enough to Break the PU's Bohemia has a plurality of electors. They took my electoral vote away. So I can't really influence elections any more. and fighting the HRE Emperoro is a pain in the ass even with France on your side. It seems all the doomstacks come after me and It doesn't care if my allies own their territory. Fighting these unbreakable vassal/allies is a pain.