It's three down, one more to go: the debates in the U.S. Senate race in Massachusetts. On Oct. 10, Scott Brown and Elizabeth Warren continued to make their case on issues ranging from jobs to education. But one of the stars of the debate wasn't even in the room. He's not even a candidate or a member of Congress. He's the conservative activist and anti-tax crusader Grover Norquist, a power broker who makes or breaks careers — even those of veteran Republicans. Norquist has gotten nearly every Republican congressman and senator to sign a pledge not to raise taxes on anyone under any circumstances.

In the Springfield debate, Warren mentioned Norquist's name three times. One of the mentions:

"Sen. Brown has taken the Norquist pledge, making sure he has said he will not raise taxes by $1 on millionaires on billionaires on big oil. And that’s exactly what he voted for. So on the Buffet rule, asking billionaires to pay a fair share, to pay what their secretaries pay, Sen. Brown voted with the billionaires.”

Warren dropped Norquist's name again 3 minutes later, saying, "I think I heard Sen. Brown say instead of working for the people of Massachusetts, he's made a pledge to work for Grover Norquist. … What Sen. Brown has said he would do is let more than $2 trillion tax cuts expire for 98 percent of the families here in Massachusetts."

Brown signed Norquist’s Taxpayer Protection Pledge 2 years ago on his way to defeating Martha Coakley in the special election. During the Oct. 10 debate, he proudly stood by the pledge: "Listen, I'm glad Grover Norquist agrees with me. We shouldn't be raising taxes on anybody in the middle of a 3 1/2 year recession. Let’s make it clear. I’m not going to be raising taxes on anyone in Massachusetts or anyone in the United States.”

After the debate, Warren's campaign sent out an email. The subject line is "Warren stands with Massachusetts women, Brown stands with Grover Norquist."

Between now and Election Day, Warren will try to poke holes in his image as a bipartisan bridge-builder. For his part, Brown is fighting for the state’s moderate voters to hold on to his seat.