French king elected HRE's emperor

During the centuries, several French kings tried to be elected Holy Roman Emperor, or were at least suggested - Philipp III (candidating against Ottokar Przemysl and Rudolf Habsburg) and Francis I come to my mind. As we know it didn't happen.

What would've been necessary to put a French king on the HRE's throne? Maybe we can combine that with my idea about an English-Castille union... though I don't know what a French king could achieve as emperor, since the emperor hadn't that much real power. Most French kings just used that situation to grab some bits of the HRE for France, piece for piece... But as I said, some kings actually candidated, so I guess they must've had some plan. But what would they do after being elected?

The HR Emperor might not have had much power (not after Frederick II., anyways), but, ah, suddenly he would have had a HUGE royal domain (that beinng France)k, so to say, with which to enforce his imperial power against the varous princes and princelings...

Only the latter French kings - even at the times of Louis XI the vassals still had much power in France. The fact that they were closely related to the royals didn't make things better. So or so: The Habsburg emperors (at least those who also governed Spain, frex Karl V) had to promise at their election that they wouldn't do what you suggested. (If it wasn't like that, unification of Germany would've been easier.) If they don't want to make such a promise - they aren't elected. Unless some people in Germany like the idea to be incorporated into France.

Were talking about late middle age/erly modern age here. Not everything has to go the regular way. Say, for whatever reason there is a split in teh electorate... a religious question would make sense, and the three archbishop-electors are overvoted by the rest. Then the three archbishop-electors elect the French King as anti-emperor. Of course the Frenc King would have to be ambitious enough to actually go fo rit instead of just using the situation to grab more land, but thats hardly without the limits of plausibility...

So, in short, IMO, its sill very well possible.

If the Fuger hadn't lent so much money to Charles of Hapsburg, or if the Medicis had matched the Fuger, Francis I would have won. It was close in the end.