Donald Trump, who says many stupid things, revaleed the secret at the recent debate (courtesy of Talking Points Memo, from a piece entitled "The Real reason Donald Trump Embarrasses the GOP"):
So why is Trump the enemy, really? The GOP will say it’s because he’s a clown, he has no experience, he can't win, he’s more a celebrity than a politician. This might all be true. But there’s another big reason they’d rather not talk about.
At the debate and numerous public appearances, Trump has matter-of-factly stated that he is an equal opportunity donor to Republican and Democratic candidates—not for the purpose of civic duty or altruism, but in exchange for influence. He has openly deemed his gifts to politicians a business expense. He went so far as to declare, before 24 million viewers at the debate, that he uses his donations to obtain favors from legislators who are all too eager to bow to his requests. He not-so-subtly implies that politicians are bought and paid for by him and other financial moguls. And he expects a fair return for those dollars, measured in policy rewards like zoning adjustments, subsidies for building projects and long-term tax relief.
In short, he lets the cat out of the bag about something the political system has spent more than a century to disguise.
Representative democracy can only remain legitimate in the eyes of its citizens if they believe that those who seek and hold public office are independent actors. We have tolerated well-funded lobbying organizations, most of which get their money from rich donors and corporate investments. Hillary Clinton admits she receives huge contributions to her campaign from Wall Street titans. But she adamantly denies that these millions of dollars influence her political decisions.