Meet Hillary Clinton's New Campaign Weapon — Bill

At a Manchester, N.H., watch party following Saturday's Democratic primary debate, Hillary Clinton stood side by side with the man she called her "not so secret weapon" — her husband, former President Bill Clinton. Voters are about to see much more of him, she said.

"We're going to cover as much ground in New Hampshire as we possibly can," Clinton said. "See as many people, thank everyone who's going to turn out and vote for me to try to get some more to join them."

Bill Clinton said he was "proud" of his wife, and he told New Hampshire voters "we got to be out there every single day" after the New Year.

Family members of candidates are the most valuable validators a politician running for higher office can have. They presumably know the candidate better than anyone. Usually the family member is a child — think Ivanka Trump — or a spouse — a female spouse. This year, voters have seen Donald Trump's wife, Melania, at campaign events. Heidi Cruz is campaigning full throttle for her husband, Ted Cruz. Candy Carson sang the national anthem at a campaign event for her husband, Ben Carson. But on the Democratic side, Hillary Clinton has a spouse like no other — her husband, otherwise known as former President Bill Clinton.

So far Bill Clinton's appearances on the campaign trail have been confined to cameos — he was the warm-up act for Katy Perry at a rally for Hillary in Des Moines, Iowa, in October, when he put his own twist on the glass ceiling.

"I want to talk about one barrier that has not been broken," the 42nd president said. "I want you to support Hillary for me, too. I want to break a ceiling. I'm tired of the stranglehold that women have had on the job of presidential spouse. I want you to help me deal with that."

Having a former president as a campaign spouse is unprecedented in U.S. politics.

Not only is there no model for a former president as presidential candidate spouse, but Bill Clinton also happens to be preternaturally talented on the stump — one of the best retail politicians of his generation. And voters have fond memories of the Clinton years — peace , prosperity and no big terror attacks.

So far this year, Bill Clinton has been nothing but a plus. He's the subject of warm and fuzzy interviews like this one Hillary Clinton did recently with late night comedian Jimmy Kimmel. The weighty subject — if she becomes president what should HE be called?

But nothing involving Bill Clinton is ever that simple. He is a huge celebrity and a talented communicator in a class by himself but he also has the potential to overshadow his wife, who is a more pedestrian performer on the stump. Donna Brazile, who was Al Gore's campaign manager, worries about this. Brazile said "one of the most important things he can do in this election cycle is to basically stay out of the way. Let Hillary Clinton make the case for herself. Allow Hillary Clinton to talk about her vision for the country."

The Clinton campaign wants to keep the focus on Hillary and is trying to make it clear that Hillary is not offering a "buy one get one free" deal.

They've learned from bitter experience. During the Democratic primary in 2008, Bill Clinton tried to defend his wife with strident attacks on Barack Obama that backfired .

Clinton's campaign aides say Bill Clinton's role this time around is very clear. He's not involved in the day-to-day campaign but he is a sounding board for Hillary and daily source of advice on what voters are thinking and how best to communicate with them about their concerns.

Bill Clinton remains the most sought-after surrogate in the Democratic Party and the Clinton campaign will be using him where and how he can do the most good.

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