The story
From the sentiment that a mother's child has gone to heaven and is now an angel. In 2000 the organization Angel Moms was founded, a group of mothers whose children had died, not limited to a specific cause. In the second sense the term was introduced by Donald Trump on August 31, 2016 at the end of a speech about illegal immigration. He invited mothers whose children had been killed by illegal immigrants to speak on stage and share their experiences.
Etymology from Wiktionary, CC BY-SA 4.0.