Power per se doesn't corrupt: Thing is, with power comes privilege. People then tend to take measures to preserve their own power, if only for the perks.
It doesn't automatically soil and corrupt them: For examle, A left-wing, populist leader may cling to power by introducing popular, pro-worker reforms to boost his own influence and ensure his re-election. Although this hypothetical democratic leftist is indeed preserving his power/privilege, he isn't actually becoming corrupted by it.
Bourgeois power does corrupt: Bourgeois leaders rule on behalf of the propertied elites. Ultimately, they hold the leash: The bourgeoisie owns the mass media and they largely control public discourse: If a politician went rogue, they'd discredit him. If it didn't work, they might deliberately sabotage the economy to create unrest. If it still didn't work, they'd fund a military coup to overthrow the regime and implement dictatorial class rule.
Reformist politicians then must then sell out the people over and over to cater to the interests of the ultimate owners of the scheme.


Society does not consist of individuals but expresses the sum of interrelations, the relations within which these individuals stand. ~ Karl Marx
