This blistering resignation letter from a White House adviser is a must-read.

When Elizabeth Holtzman was in Congress, she helped write the Refugee Act, which has guided the U.S.'s principles on the issue for nearly four decades.

In more recent years, she's been serving on the Homeland Security Advisory Council, a bipartisan team of experts that advises presidential administrations. That council includes a committee which, in 2016, called for the end of for-profit immigration detention facilities — an issue front and center in Trump's support of family separation policies.

Holtzman is a Democrat, but she's a stateswoman first and foremost. She's joined four other council members who are resigning in protest of Trump's immigration policies, and her powerful resignation to Secretary of Homeland Security Kirstjen Nielsen letter is a must-read.

The letter is a call to arms that recalls America's progress on how we treat refugees and immigrants, and how we're now squandering that away in catastrophic fashion.

"There was a time that the U.S. welcomed refugees," Holtzman wrote.

She pointed out that the Refugee Act was created in the aftermath of our country's failure to properly take in Jewish people and other marginalized groups fleeing the Holocaust. Holtzman dropped some hefty numbers: 750,000 refugees taken in from Vietnam, 600,000 from Cuba, and 100,000 Jewish refugees who fled the Soviet Union.

She argued that the shift in policy is not only immoral, but also in direct violation of the Refugee Act: "Considering that history, the thought that the U.S. government is afraid today of 2,000 children and their parents is both laughable and appalling."

She's resigning, but she wishes it were someone else.

Technically, her letter is written to Nielsen, and that’s heavy enough. But it’s clearly a shot at Trump as well.

"Although it is I who am resigning in protest against these policies, it is you who should be tendering your resignation instead," Holtzman wrote to Nielsen.

Yes, the letter is a scathing indictment of Trump's family separation policy, something nearly 70% of Americans oppose. But it's also about something more: The U.S. is abdicating its moral leadership on vital humanitarian issues at a time when we should be doubling down on doing the right thing.

Consider this letter the new inspirational poster to pin to our walls, serving as a reminder of how great we've been, and can be if we stand up for what's right.

Correction 7/23/2018: An earlier version of this story mistook who Holtzman was asking to resign; it has been updated for clarity.