In another sign of the degree to which Dem hopes of holding the Senate turn on the increasingly brutal battle for women, the DSCC is out with a new ad that savages Colorado GOP Senate candidate Cory Gardner’s gyrations on Personhood, which holds that full human rights begin at the moment of fertilization.

Gardner has attempted to soften his stance by disavowing his previous support for a state Personhood measure and coming out in support of over-the-counter contraception. But Gardner still supports a federal Personhood measure that could potentially restrict some forms of birth conrol.

Here’s one way to understand the battle for the female vote. It’s often discussed in terms of the “gender gap,” i.e., the margin any given Democratic candidate enjoys among women. That’s important, but Dems are also eying another key goal: How to drive up the share of the 2014 electorate that women represent.

Democratic strategists familiar with the hardest fought and probably most critical Senate races — in Colorado, Iowa, North Carolina, and Arkansas — all tend to gravitate towards citing 53 percent as an important, if approximate, threshold. That is, they privately say that if the electorates in their states approach 53 percent women, and their candidates enjoy a reasonable advantage among them (as some polls suggest they do already), then their chances of winning improve.

This is key to Dem hopes of making the electorate look more like it did in 2012 than in 2010. While replicating the 2012 electorate is very likely impossible, given that multiple polls show core GOP groups a lot more revved up for this fall, a lot turns on whether Dems can push the composition of the electorate even marginally in their direction. Women are central to this, because Republicans enjoy an advantage among men, who tend to be reliable voters in midterms.

Political scientist Michael McDonald, who heads the United States Elections Project and studies voting patterns, suggests a way of understanding this. He says census data indicates that in 2010, women represented 52.7 percent of the national electorate; in 2012, they represented 53.7 percent — a full percentage point higher. Such differences may not seem like much, but they could prove significant.

“In some of these Senate elections, every percentage point is going to matter,” McDonald tells me. “The margin is so narrow that the Democrats are looking to eke out victory by shifting the composition of the electorate by even a percentage point among key demographic subgroups.”

Not only that, but it matters which women Democrats are able to turn out. Hence the relentless focus on single women, who are more inclined to vote Democratic than GOP-aligned married women, and are more inclined to sit out midterms.

“The high propensity voter is already baked in,” McDonald says, referring to married women. “If Democrats are going to juice up that gender number, they’re going to be looking for moderate propensity voters, or single women.” Thus the relentless focus on Personhood and women’s economic issues.

Whether Democrats keep the Senate really could come down to whether they can grind out the smallest of victories on the margins.