OpenSecrets is a non-profit organization that tracks money in politics. Their website, OpenSecrets.org, provides a wealth of information on political donations, lobbying, and campaign finance. One of the features of OpenSecrets.org is an app called "Who Paid For That?" which allows users to track the source of political advertisements.

To use the "Who Paid For That?" app, simply enter the name of the candidate or organization that you are interested in. The app will then provide a list of all of the political advertisements that have been run by that entity, as well as the amount of money that was spent on each ad. The app also provides information on the source of the funding for each ad, including the names of the donors who contributed to the campaign.

The "Who Paid For That?" app is a valuable tool for anyone who wants to track the source of political advertising. It is an easy-to-use app that provides a wealth of information on campaign finance.