Thousands of people on Wednesday turned out across the U.S. to protest President Trump’s flurry of early actions, denouncing his plans for mass deportations, his attacks on diversity initiatives and his efforts to restrict transgender rights.

The demonstrations, which popped up in major cities and state capitals in more than a dozen states, appear to have been spurred online, with word spreading via hashtags such as “#BuildtheResistance.” They were loosely organized under an unofficial tagline — 50501, to represent a goal of 50 protests in 50 states on one day, according to various websites and social media accounts. Most demonstrations began in the afternoon at Capitol buildings and at city halls.

Those involved say that the movement is meant to protest Mr. Trump’s early actions and Project 2025, the conservative policy blueprint that Mr. Trump sought to distance himself from during the campaign. Many of his plans so far are aligned with Project 2025 proposals.

The demonstrations gained momentum this week on social media platforms including Reddit, Instagram, TikTok and X, the social media site owned by Elon Musk, the world’s richest man and a close adviser to Mr. Trump. Mr. Musk’s own moves — leading a team that has aggressively pushed into the systems of a number of government agencies and attempted to shutter at least one wholesale — have also prompted protests.

Carrie Rheingans, a Democratic state representative in Michigan who spoke at the protests in Lansing, said people from across the state gathered at the Capitol in below freezing temperatures. She added that the protests came together over 48 hours and were organized by people who “couldn’t take it anymore.”