Ahead of the 2016 presidential election, plenty of Republicans from foreign policy and national security circles were willing to publicly break ranks and announce their opposition to Donald Trump's candidacy. At one point, 50 of them even signed a letter declaring that the Republican nominee lacked "the character, values and experience" to be president and "would put at risk our country's national security and well-being."

Four years later, their numbers appear to have grown -- and they're urging Americans to vote for Joe Biden.

More than 80 career national security professionals have signed an open letter of support for Democratic presidential candidate Joe Biden, saying that President Trump "has created an existential danger to the United States." Most of the signatories, who include career diplomats, intelligence officers and defense policymakers, have served both Republican and Democratic administrations.

The group, referring to itself as the "Steady State," published this online letter, calling not only for Biden's election, but also condemning Trump for creating "an existential danger to the United States." The joint statement added that the incumbent president's re-election would likely bring "catastrophic results."

And while the rhetoric was striking in its intensity, so too were some of the names who agreed to endorse the missive. As the Post's report noted, Doug Wise, a former CIA clandestine officer and former deputy director of the Defense Intelligence Agency, "broke a career-long vow to serve in silence by signing the letter." Wise, who said he leans Republican, had never even voted in a presidential election before, but he'll vote for Biden in the fall.

The Post also spoke to Margaret Henoch, a former CIA officer, who agreed that a public presidential endorsement like this one is "absolutely" unheard of for career professionals -- but she believes these are not normal times.

In the short term, an effort like this isn't likely to have a significant impact. In fact, given the circumstances, most Americans probably won't even hear about the "Steady State" letter. But in the fall, when the Biden campaign reaches out to disaffected GOP voters, don't be surprised if this rises to the fore.