Complex sentence: They claim that as all campaigns need donations, the candidates who hold policies viewed as unfavorable by corporate interests and wealthy individuals will be denied funding, and that thereby the system in actuality ends up forcing politicians to change their policies to suit the current business environment.
Split into simpler sentences: They claim that as all campaigns need donations, the candidates who hold policies viewed as unfavorable by corporate interests and wealthy individuals will be denied funding. Therefore the system actually ends up forcing politicians to change their policies to suit the current business environment.