Fox News promoted an anti-Hillary Clinton ad created by American Crossroads, a conservative Super PAC co-founded by Fox News contributor Karl Rove.

On the April 14 edition of Fox News' The Five, co-host Kimberly Guilfoyle praised a new American Crossroads ad, comparing Hillary Clinton to Richard Nixon. After playing nearly the entire ad, Guilfoyle claimed the “dramatic attack ad” came from the “conservative Super PAC American Crossroads,” but did not disclose any other information about the group:

KIMBERLY GUILFOYLE (CO-HOST): Sanders got some unsolicited help today from conservative Super PAC American Crossroads. They put out a dramatic attack ad, depicting his opponent as a modern day Richard Nixon.

[...]

ED HENRY: I think it is important that you mentioned the context of the general election in terms of that American Crossroads ad, that’s a conservative group who will undoubtedly be pounding Hillary Clinton if she is the Democratic nominee, talking about the e-mails. But that's a stark contrast to what we are likely to see tonight. Bernie Sanders said at the very beginning of the first debate, he was taking the e-mails off the table. Very few debate moderators have pressed Hillary Clinton over the course of the last several months on that issue. Although there was a little hint from the Sanders camp today that you had both of these candidates yesterday on the picket lines with striking Verizon workers in the New York City area and the Sanders camp was saying, wait a second. It turned out Hillary Clinton was with the workers yesterday. But back in 2013 she gave one of those big paid speeches, over $200,000 paid for by, yes, Verizon. So she was standing up to the company yesterday, on behalf of the workers, but it turns out a couple years ago, was making big money from the company.

Guilfoyle failed to disclose that American Crossroads was co-founded by Fox News political contributor Karl Rove. He joined the network in 2008, and helped create the Super PAC in 2010 where he still serves as an “informal adviser.”

Fox News has a history of failing to disclose the ties of its hosts and contributors. And during the September 21, 2014 edition of Fox News Sunday, host Chris Wallace invited Karl Rove to discuss the 2014 midterm Senate races, without disclosing Rove's super PACs that poured millions into influencing the outcomes of the Senate races Rove was invited to discuss.