See this Sacramento Bee story on how three independent expenditure committees will spend tens of millions to support Jerry Brown in his race against likely nominee Meg Whitman and Barbara Boxer in her attempt to survive the fall race against the GOP nominee.
This is union and special interest money, and it has always been in play, swamping the GOP candidates except for those few who could use their own resources like Whitman. Citizens United allows candidates who are not themselves wealthy at least a hope of support from corporations and wealthy individuals.
No wonder President Obama and the Congressional Democrats hate the decision so much. It was much easier when only the special interests they controlled could spend heavily in key races and states.