It is one of the more unusual battle lines in the culture wars.
Liberals, it is said, have a baby problem. They don't have enough of them, compared to conservatives. And this failure to replenish their ranks is a reason why they lose elections. Call it a fertility gap.
"The political right is having a lot more kids than the political left," Syracuse University professor Arthur Brooks says. "The gap is actually 41 percent."
Studying numbers from the General Social Survey -- a government survey of social trends -- Brooks found that 100 unrelated liberal adults have 147 children, while 100 unrelated conservatives have 208 kids.
That makes a difference, Brooks says, because "80 percent of people that express a political party preference are voting like their folks."
Hence, more Republicans.
There are many possible reasons for these lopsided numbers -- conservative opposition to birth control, the fact that city residents are more likely to be liberal and have smaller families.
Nevertheless, conservatives such as pollster Kellyanne Conway relished this theory about depleted Democrats.
"They're for abortion policy, they're for same-sex marriage, they're for many of the agenda items that eventually mean you probably don't have children in the household," Conway said.
And Democrats such as Jenny Backus -- doing her small part by expecting her firstborn this October -- looked for the silver lining.
"It's something that you can always encourage your friends when you're doing a little matchmaking, to say, 'Hey, we got to make sure we close the fertility gap,'" she said.
Conway saw another good side to the story for conservatives.
"It completely demystifies the fact that Republicans aren't having sex," she said. "Unless every Republican is procreating in a petri dish, ah ha, we too know how to have fun."
And it could mean another area of competition between the two parties.
"They have laid a baby gauntlet and we're going to pick it up and go with it," Backus said. "I think this is going to be great talk in intern happy hours all over Washington D.C."
Brooks is dead serious about this. He says the baby gap will influence future elections. His message to liberals dismayed with his findings: "Have babies! Forgo the cat, have kids."