MADISON, Wis.  The fury among thousands of workers, students and union supporters rose to a boil on Thursday, as state lawmakers prepared to vote on landmark legislation that would slash collective bargaining rights for public workers. Protesters blocked a door to the Senate chambers. They sat down, body against body, filling a corridor. They chanted “Freedom, democracy, unions!” in the stately gallery as the senators convened.

Then the surprising drama in Madison this week added a new twist: the Democrats disappeared.

That left Republicans, who control the Capitol and had expected to push through the bill, in limbo. Although Republicans control the State Senate by 19 to 14, 20 senators  and thus, at least a single Democrat  must be in the room to call a vote on such fiscal matters.

“It’s disgraceful that people who are paid to be here have decided to skip town,” Senator Michael Ellis, the Senate president, said shortly after the roll was called. Said another Republican leader, Senator Scott Fitzgerald, “This is the ultimate shutdown.”