There are limits on how much money someone can donate to a campaign, and it's not like Bernie is hurting for money, so I don't know what point you are trying to make.
And I spent many years working in politics at the National level, so I think I have a pretty good understanding of It in general.
There are relative limits to anything's effectiveness. This doesn't change the fact that these things are
1. perversions of clearly representing the will of the people.
2. Has largely been responsible for influencing and warping public perception for decades, and a key driver in slowing progress in the United States.
3. Must be ripped out at their roots in order to preserve democracy and a functionality representative society over the long term.
The issue is that you don't seem to view the system itself as culpable for the degradation of norms and proper representation within the country. You don't view the political/media/financing system itself as a core problem in the country, and it absolutely is.
'Well Sanders is getting his message out' is cold comfort when the media, through centralized ownership and a desire to maintain a malignant status quo, also has had a proven record of discriminating against Sanders like candidates that try to upend the donor and influence controlled systems.
You don't see how candidates parrot pro profit Health Care industry talking points influences perception before a citizen even gets to the ballot booth? And, generally speaking, how these corporations that are donating, influencing, and misdirecting are doing spin favor of themselves and not the people of the country? It's the whole reason that corporations routinely end up skirting (if not outright breaking) regulations whenever higher profits can be attained versus the health of the people. Corporations only exist, functionally, for the betterment of itself, not society. People are malleable and prone to conditioning/suggestion, it's exactly why corporations buy politicians and spend billions of psychological research for advertising, because it works.
