Elon Musk posted a cryptic message about the "No Kings" protests after activists took to the streets across the U.S. over the weekend.

Democracy is “in real trouble,” Mark Ruffalo told MSNBC’s Antonio Hylton while attending the “No Kings” rally in New York City Saturday. His words were echoed by Ellen Pompeo, Kerry Washington, Jimmy Kimmel, and many more notable people and celebrities who spoke out in support of the nationwide protests.

Phoenix's "No Kings Day" rally against President Trump, one of many nationwide, coincided with his 79th birthday and military parade in Washington, D.C.

A crowd-size expert from the U.K. estimates that between 10,000 to 15,000 people attended Saturday's protest in downtown Chicago. But some estimates say 75,000 people gathered downtown.

We implore everyone not to play into Trump’s hands and fall for his schemes,” the chair of the Washington State Democratic Party said in a statement.

The "No Kings Nationwide Day of Defiance" is planned to "reject corrupt, authoritarian politics in the United States," organizers say.

NBC News' Jacob Soboroff reports from Los Angeles City Hall where thousands of protesters have gathered for a 'No Kings' protest against the Trump administration and ahead of the president's Washington D.