When throngs of abortion protesters convene Friday for the annual March for Life, they will enjoy the warmest show of White House support in the event's four-decade history.

Vice President Mike Pence and top Trump adviser Kellyanne Conway will headline the pre-march rally on the National Mall, becoming the highest-ranking members of a presidential administration ever to speak at the annual protest. President Trump was expected to call in to the rally to voice his support, but is no longer doing so.

Pence and Conway's presence is a huge boon to the march, attended by hundreds of thousands of people every year who want to register their opposition to the Supreme Court's 1973 Roe v. Wade decision legalizing abortion. It further solidifies their confidence that President Trump will live up to his promises to crack down on abortion, as he vowed during his campaign.

Pence is a favorite of conservatives for his actions as Indiana governor and as a member of Congress to limit abortion. While Trump used to support abortion rights, activists view Pence as one of their own, a longtime and trustworthy ally.

"He's not a recent convert to caring about issues of human dignity," said Russell Moore, president of the Ethics and Religions Liberty Commission, the public policy arm of the Southern Baptist Convention. "He's been in the trenches for a long time and is deeply admired by all of us."

Conway also infused abortion foes with hope in the fall, when Trump picked her to manage his campaign. Conway has long advocated against abortion and advised conservatives on how to effectively address the issue.

"Making the March for Life a major priority during her first week of the new administration gives great hope to pro-life Americans," said March for Life President Jeanne Mancini.

The warm nod from the White House is especially significant to activists who have participated in the March for Life for decades but never got to see a vice president or president speak in person.

Chuck Donovan, who has attended the march for about 30 years, recalls one year when President Ronald Reagan called into the rally while standing on the Ellipse outside the White House. It was Reagan's compromise for march organizers, who had intensively lobbied him to attend in-person despite security concerns.

"To my knowledge, that is as close to the march as any president has ever come," said Donovan, who now heads the research arm for the Susan B. Anthony List and has worked in the anti-abortion movement for decades.

"Vice President Pence will be a whole lot closer," Donovan said.

White House press secretary Sean Spicer had said earlier this week that there will be a "heavy administration presence."

For however they feel privately about Trump, his victory has infused abortion opponents with fresh hope. Congress is now seriously discussing an Obamacare repeal measure that would ban Planned Parenthood clinics from receiving Medicaid dollars. And Trump has said next week he will nominate a justice to the Supreme Court who opposes abortion.

Participants are also trying to draw a contrast between the March for Life and a widely attended women's march on Saturday, which conservatives complained mostly centered around policy priorities of liberals and shut out women who oppose abortion.

"Noticeably missing from the women's march was the most prominent woman in the White House and guess where she's going to be — March for Life," said Ashley McGuire, senior fellow at the Catholic Association.

Moore said March for Life is "more inclusive" than the women's march.

"Walk around and there are secular humanist pro-life groups and LGBT pro-life groups and Hindu pro-life groups and a great deal of diversity of people who disagree on other things," Moore said.