It was shaping up to be one of the most expensive Senate races in U.S. history. By this January, Republican Scott Brown and Democrat Elizabeth Warren of Massachusetts each had raised millions in their contest for Brown’s U.S. Senate seat, and third-party groups were spending even more on negative ads.

Both candidates had publicly tried to distance themselves from the so-called super PACs and other big spenders. On January 23, Brown and Warren put their money where their mouths were: they signed a “People’s Pledge” designed to end the influence of outside spending in the campaign.