Ken Vogel in Politico:

Big-money outside groups have spent more than $143 million in the presidential race in the six months since any of them were required to reveal their donors, according to a POLITICO analysis of campaign and advertising records.

The origins of some of that cash will never be revealed, while the rest of it won’t become known until midnight on Jan. 31 ― meaning that voters won’t know who funded the majority of the ads in the presidential race until just hours before Iowa voters head to their state’s pivotal caucuses.