WASHINGTON — Presidential candidate Michele Bachmann’s pro-life message has been one that resonates with her socially conservative supporters. Over the weekend, she used it to take on the presidential race’s front-runner.

Last week, several Republican presidential candidates, including Bachmann and former Minnesota Gov. Tim Pawlenty, signed the Susan B. Anthony List’s “Pro-Life Presidential Leadership Pledge,” a four-part pact that had the candidates affirm their support for pro-life policies.

Former Massachusetts Gov. Mitt Romney, who polls show to be the leader in the race, did not sign the pledge, opening the door for criticism from the field’s conservatives.

"It is distressing that Governor Romney refuses to sign the SBA Pledge, even while claiming to be pro-life. The excuses for not signing clearly continue the doubts about his leadership and commitment to ending the practice of abortion — particularly for a candidate who ran as pro-choice for the Senate and Governorship of Massachusetts,” said a statement from the Bachmann campaign.

“Any Presidential candidate seeking our party's nomination should sign the SBA Pledge and vow to protect life from conception to natural death. Governor Romney should reconsider his decision not to sign the Pledge just as he reconsidered his position on the life issue during the last campaign."

Romney was quick to defend his decision not to sign. In a Saturday op-ed for the National Review, Romney committed to pursuing pro-life policies, but he said the pledge is “well-meaning [but] overly broad and would have unintended consequences.”

Thus far, Republican presidential candidates have kept their focus on fiscal issues, an area where Romney has been most comfortable.

But if Bachmann is able to make the race about social issues like abortion and gay marriage, she stands to gain. Bachmann is a popular figure among social conservatives, a group Romney has struggled to court. During speeches before the religious Faith and Freedom Coalition this month, Bachmann gave a fiery address about her history advocating for socially conservative causes, while Romney focused almost entirely on fiscal policy.

Romney’s op-ed walks readers through his support for pro-life policies, but on this issue, he’ll certainly be asked to respond to the barrage of attacks from more outspoken conservatives as the race moves on.

Devin Henry can be reached at dhenry@minnpost.com.