Back in January, Republican Sen. Scott Brown and his Senate opponent, Elizabeth Warren, signed a pledge to effectively ban or neutralize outside money — saying that they would donate to charity if a group advertised for them or against their opponent. Brown, who faced a tough 2010 special election for this reason, fought for the deal — which was initially seen as a coup for him because of his war chest. But since then, Warren has had one very prime weak spot — her ancestry controversy — that outside groups weren’t able to exploit because of the document above. Plus, she’s become a huge fundraiser in her own right. So Brown is suddenly having regrets. But is this an example that other campaigns can follow?