A crowd estimated in at least the tens of thousands flooded the National Mall for the March for Life on Friday.

The annual gathering draws pro-life advocates from all over the U.S. and foreign countries to Washington, D.C., marking the anniversary of the Supreme Court's Jan. 22, 1973 decision that legalized abortion.

The march was kicked off by a rally on the National Mall attended by thousands, where President Donald Trump became the first U.S. president to address the March for Life. He did so while Democratic House trial managers were making the case for his impeachment in the U.S. Senate.

"Unborn children have never had a stronger defender in the White House," Trump said. "Every life brings love into this world. Every child brings joy to a family. Every person is worth protecting."

The president highlighted recent state-level efforts to expand abortion to include all nine months of pregnancy, singling out legislation passed in New York last year as well as controversial comments by Virginia Governor Ralph Northam (D).

Trump was joined on stage by Sen. Mike Lee (R-Utah), March for Life president Jeanne Mancini, Marjorie Dannenfelser of Susan B. Anthony List, and Sen. James Lankford (R-Okla.), and others.

Other speakers at the rally included political figures from both Republican and Democratic parties: the First Lady of Louisiana, Donna Bel Edwards; House Minority WHIP Rep. Steve Scalise (R-La.); Louisiana State Sen. Katrina Jackson (D); U.S. Rep. Chris Smith (R-N.J.); and Marjorie Dannenfelser, president of the pro-life group Susan B. Anthony List and co-chair of the Trump 2020 campaign's pro-life coalition.

"Today, as President of the United States, I am truly proud to stand with you," Trump said at the rally, noting that the March was "to defend the right of every child, born and unborn, to fulfill their God-given potential."

"Every child is a precious and sacred gift from God," he said.

Following the speeches from the rally's main stage, the march proper began, progressing up the National Mall towards the Supreme Court.

Carrying the giant March for Life banner at the front of the crowd is regarded as a privilege, bestowed on a different group each year.

For 2020, students at Oakcrest School in McLean, Virginia-a Catholic all-girls middle and high school-led the march. Oakcrest administrators said that the school had a long history of supporting life and participating in the march each year, with classes suspended for the day to allow students and teachers to attend. The banner was carried by members of the school's student-run Respect Life Club.

Behind Oakcrest, students at Colorado Christian University carried flags ahead of the main body of the march. The estimated tens of thousands of marchers moved up the National Mall towards the Supreme Court on Capitol Hill were a few hundred pro-abortion demonstrators had gathered earlier in the day.

Now in its forty-seveth year, the theme of the 2020 march,"Life Empowers: Pro-Life is Pro-Woman," was chosen to mark the centennial anniversay of women's right to vote in the United States with the ratification of the 19th Amendment in 1920. The march's theme was chosen to counter the narrative put forward by abortion supporters that the practice "empowers" women. 

Jeanne Mancini, president of the March for Life, told CNA when the theme was announced that "we primarily chose it because of the centennial" and to show that real "empowerment" meant valuing the lives of mothers and their unborn children.

In an op-ed published Friday morning, Mancini said that "abortion does not improve the lives of women and, unlike many who claim to be part of the women's movement today, the suffragists wanted no part of it."

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"Abortion not only destroys women's offspring, it can also cause lasting physical harm and psychological trauma. It's a violent step backward that disproportionately affects women," Mancini said.

"It has been 100 years since the suffragists won women the right to vote. They did so over time with single-minded focus and perseverance, and, in the end, gave voice to their voiceless sisters."

"We should not take for granted the progress they made. This November, we should use their victory to give voice to the voiceless unborn. They too deserve equal rights and protection under the law," said Mancini.