The event is the largest annual gathering in the United States of opponents of the Supreme Court's 1973 ruling in Roe v. Wade. That ruling found that certain state laws outlawing abortion were an unconstitutional violation of a woman's right to privacy, effectively legalizing abortion nationwide.
"As president, I will always defend the first right in our Declaration of Independence, the right to life," Trump said in remarks recorded in the Oval Office, a right he said extended to "unborn children."
Vice President Mike Pence appeared onstage at the rally to introduce the video, calling Trump, who before entering politics said he supported abortion access, "the most pro-life president in American history."