This. As a matter of principle there should be no corporate money in politics. Whether boycotting is the way to go, that's a separate issue - I personally don't think it's enough, but it's better than nothing. This goes for both parties - lobbying and donating to a political cause at corporate level should be completely banned.
Or, if you want to level the playing field to some minor extent, make every corporate donation or lobbying effort a matter of company-wide vote. If the majority of the firm says yes, donate. And cap the size of the donation at a fixed number per company.
But really just keep it simple and make it illegal. It's one of the things today with the widest, most astonishing gap between how bad it is and how much people actually know and care about it.