U.S. Senator Jeff Merkley is speaking through the night about President Donald Trump and threats to democracy.

The Oregon Democrat is going to hold the Senate floor tonight as long as he’s able to keep speaking. He began standing behind a poster that says, “Ring the alarm bells: authoritarianism is here now!”

Merkley, who is 68, is warning that Trump’s moves since taking office amount to an authoritarian seizure of power. He has also criticized the Supreme Court for not putting more limits on presidential power.

“We are in the most perilous moment for our Constitution, the biggest threat to our republic since the Civil War,” Merkley said.

He also accused Trump of using the U.S. Justice Department to target political enemies, and of trying to pressure the media to influence its coverage.

Since Trump became president this year, Senate Democrats have engaged in several marathon speeches to protest his actions.