@ledoian @kaia Most influential (or powerful) seems like an annoyingly tricky question because there's so many way of overruling others in politics.

Like in France, Prime Minister can choose to ignore the assembly/senate (and this has been done quite frequently these last years) but assembly can do a vote of no-confidence (with majority of votes) to effectively kick out the Prime Minister.
At least for France the President holds a *lot* of power so in this particular case it's easy (unless somehow we do a Belgium, just President instead of Prime Minister).