Democratic senator holds floor in 15-hour speech to criticize Supreme Court nominee Neil Gorsuch

"So much is at stake in terms of the legitimacy of the court," he said.

Merkley, D-Ore., spent much of his time going through Gorsuch's record on the bench and talking about the importance of appointing moderate judges to the highest court in the country.

Many Democrats say they believe Gorsuch is too extreme in his strict interpretations of the Constitution to serve on the Supreme Court.

They point to cases in which he sided with employers over employees and ruled in favor of allowing private companies to claim religious exemptions from providing contraception insurance coverage to employees.

"I'm here at 4:20 in the morning because so much is at stake in terms of the legitimacy of the court," Merkley said as he stood on the floor surrounded by a few charts to help keep him on track.

Merkley began his marathon speech around 6:45 p.m. Tuesday and yielded the floor around 10 this morning, more than 15 hours later.

While Merkley's marathon speech was a galvanizing factor for progressives who oppose Gorsuch's nomination, it had no procedural effect because he did not delay any Senate floor action from moving forward, with the next vote not expected for more than 24 hours.

"The cloture vote will still be on Thursday," McConnell spokesman Don Stewart tweeted overnight.