Very interesting development in the race for the Massachusetts Senate Seat formerly held by John Kerry: Massachusetts Citizens for Life, the statewide anti-abortion group, is urging pro-life Democrats to change their registration to "unenrolled" so they can vote for Michael Sullivan in the Republican primary on April 30.

Sullivan, who's been endorsed by MCFL, has the strongest anti-abortion stance of any candidate in the race. Among other things, he's made it clear he doesn't believe Roe v. Wade is settled law.

According to MCFL, though, it's his take on other abortion-related issues that makes Sullivan a candidate worth supporting — whatever your party affiliation.

"Michael Sullivan ... is the only candidate who takes pro-life positions on funding, parental consent, and partial birth abortion," John Rowe, the head of MCFL's political action committee, said in a recent blog post. "You can see why the MCFL PAC has endorsed Michael Sullivan. You can see why so many of you pro-lifers across the state worked so hard to get Michael Sullivan more than twice as many signatures as he needed to get on the ballot. The next step is to be sure Michael wins the Republican primary."

To do that, Rowe says, Democratic pro-life voters should change their registration to "unenrolled" and back Sullivan in the Republican primary on April 30. It is, Rowe argues, a relatively easy move to make. And after they vote for Sullivan, he notes, those voters can immediately re-register as Democrats.

Last year, after Elizabeth Warren and a host of other pro-choice candidates won in Massachusetts, the group NARAL Pro-Choice Massachusetts announced that backing abortion rights is a recipe for local electoral success. But Anne Fox, MCFL's president, disputes that claim.

In the 2012 elections, Fox tells WGBH, "Pro-life candidates who dealt properly with the issue — who didn't duck it, and didn't pretend to be one thing when they were really something else — they won."

And in Massachusetts, Fox adds, the defeat of the so-called "Death with Dignity" ballot initiative showed that pro-life voters are a force to be reckoned with. 

"That was a huge win, because the people who voted with us were Democrats," Fox says. "It was Democrats in blue-collar cities who did that. So the potential is there."

On Greater Boston recently, Sullivan told Emily Rooney that abortion is "in the rear-view mirror" as far as voters are concerned, citing the fact that Roe v. Wade was decided four decades ago. When I asked Fox if that assessment gives her pause, she replied that focusing on Roe v. Wade is a mistake. 

"When we publish why we endorse someone, we're not looking at Roe v. Wade," Fox explained. "We're looking at abortion funding; we're looking at Obamacare; we're looking at conscience rights [for healthcare providers] ... We're looking at a bill* in the U.S. Senate right now, that's similar to bills passed in some of the states, which says that beyond 20 weeks it's irrefutable that a baby feels pain." 

Whether a Democratic pro-life push will help Sullivan beat out Winslow and Gomez for the nomination remains to be seen. But Fox says that Sullivan made the special-election ballot thanks largely to the enthusiasm of pro-life voters. ("At first, I didn't think it was possible," she says. "But our people were out there without too much of a push from us getting signatures.")

And, Fox adds, Democrats make up a higher percentage of MCFL's membership than they do of the Massachusetts electorate as a whole. If enough of them switch enrollment and participate in what's likely to be a low-turnout primary, it could be enough to put Sullivan over the top.

CORRECTION: This article originally described the fetal-pain bill as an amendment, not a standalone bill.