"Outside groups like super PACs and dark money groups have combined to spend $45 million so far in the 2020 Democratic presidential primary," Issue One research director Michael Beckel tweeted on Tuesday.
Public Citizen's analysis found that casino magnate Sheldon Adelson and his wife were the largest individual super PAC contributors since Citizens United.
The former Massachusetts governor said he would want any super PAC offering him independent support to "fully disclose" its sources of funding.
The former California Congressional candidate wants to draw more young people and people of color into the Republican Party with an anti-socialist message.
Bush's affiliated super PAC, Right to Rise, has raised $118 million, but to little effect
An examination of the small donors behind the 2016 Republican presidential candidates
The Democratic presidential frontrunner exploits a legal loophole.
Harvard law professor Lawrence Lessig's political money machine looks to Silicon Valley to save American politics