The number of Senate roll call votes on amendments — a key indicator of whether lawmakers are engaged in free and open debate — plummeted to only 18 this year, according to a review of congressional data. During the same time period in the 10 previous Congresses, senators took anywhere from 34 to 231 amendment votes.

The inaction stands in stark contrast to the promises of Senator Mitch McConnell, the majority leader. After his party took control of the Senate in 2015, Mr. McConnell vowed to end the gridlock that had gripped the chamber under his Democratic predecessor, Harry Reid, and pledged to allow both parties to offer amendments to legislation — even if it forced Republicans to risk taking politically unpopular votes.

“We’ll just take our chances,” he said at a news conference in early 2016. “You know, we’re big men and women. We’re prepared to vote on proposals that are offered from both sides.”

Instead, the Senate, once known as “the world’s greatest deliberative body,” is operating exactly as Mr. McConnell now wants it to: as an approval factory for President Trump’s judicial and administration nominees.