Part of his strategy to win the primary is to expose the donor class and their ownership of establishment candidates. This "whining" of his is accomplishing that mission.
“donor class and their ownership of establishment candidates.”
So now the Trumpsters are against Citizens United - arguably the most conservative decision of the Supreme Court in decades. To participate in our democracy, you have to be able to influence. And to influence you pay up.
Trump has chosen not to take my money and therefore he can’t whine when I boo the hell out of him if/when I see him in public.