“We have to cross a line in our thinking, not only in this state but in the country,” Mr. Gianaris said, adding that it was “mind-boggling to me that we could watch our children die and we’re sitting here making excuses.”

Twenty-nine Democrats, including all eight members of the Independent Democratic Conference, voted to consider the amendments, falling short of the 32 needed for passage. Mr. Gianaris failed to persuade a single Republican to consider the measure; more important, he also failed to lure Simcha Felder, a Brooklyn Democrat, to his side.

Mr. Felder said that he felt the bills were being rushed to the floor in piecemeal fashion.

“I do believe that its better to do something that’s as important as this in a very comprehensive way,” said Mr. Felder, who has sponsored a bill to put armed guards at schools, something he says he wished would have been taken up sooner.

“I think ‘now’ is a very broad term,” he continued, adding, “There’s a balance between doing something expeditiously or doing something immediately that’s not really conclusive, not comprehensive.”

The Independent Democratic Conference and Ms. Stewart-Cousins’ group of mainstream Democrats have tentatively pledged to form a new majority in April, after two special elections to fill seats vacated by Democrats. (That plan still depends on Mr. Felder, who has repeatedly said he is loyal to no party.)

“Those who stand on the wrong side of history on this issue will be judged harshly,” Mr. Gianaris said. “Starting with this election.”