In 2014, the right wing America Rising PAC hired Republican strategist Christine Matthews, a partner at Burning Glass Consulting, to conduct focus groups testing the Bill Clinton sex scandals, including Hillary Clinton's role in allegedly "enabling" her husband, or threatening the "other" women. The work was commissioned under the assumption that Clinton would be the Democratic nominee, and the PAC would have a ready-made opposition research file it would hand over to the Republican nominee.

The feedback: Try anything but.

"Anytime you got into the personal aspects of Hillary Clinton, it was very ineffective," said Matthews. "Women voters are of two minds about the Clinton marriage: On one level, they think she stayed with him for political reasons, which feeds the view that she's a politically calculating person. The other is, he did a lot of really bad things and she stuck through it and there's sympathy there."

But more to the point, Matthews said, female voters viewed attacks on Hillary Clinton's spouse as "inherently unfair. Ultimately, it came back down to this: Bill Clinton's not the one who's running."

When it came to criticizing Hillary Clinton as an enabler, Matthews said, the reaction was, "yeah, you're angry. It's a normal reaction. Any line of messaging on this generates sympathy for her, or voters said it was completely irrelevant."

The women in the America Rising focus group also identified areas they would consider off-limits in terms of Clinton attacks: "It was her age, her stamina, her health and her looks," Matthews recalled.