What's most surprising to many political observers is how the Sanders campaign on the Democratic side has managed to tap small donors to quickly raise large totals. As of its most recent reporting, the campaign raised $15 million from 400,000 donations from 200,000 donors. This puts it ahead of its Republican opponents. In contrast, Jeb Bush raised $11.4 million. Ted Cruz raised around $14 million. No GOP campaign matched the Sanders haul.
But there's a catch. While Sanders is creating the broadest base of financial support, recruiting donors at a much quicker rate than other insurgent candidates like Ron Paul in 2008, and out-raising his Republican opponents' official campaigns, there is another factor at play: super PACs.
These entities, created by the Citizens United Supreme Court decision, allows billionaires and corporations to effectively spend whatever they want in support of a candidate. While they are not supposed to officially coordinate with candidates, this law has been more or less openly flouted this cycle.
Bush's super PAC raised $103 million, around 10 times as much as the candidate raised through his actual campaign. Cruz's super PACs raised over $30 million, twice as much as what his campaign raised.
These numbers are evidence of the Citizens United bump, and make it so a candidate doesn't have to go out and recruit lots of small donors and actually meet lots of Americans in order to raise money. Bush's super PAC has only 9,900 donors; and they're the only fundraisers he really has to listen to.
Thanks to the Supreme Court, this is the way things are now.