MIAMI — The Florida State Senate shocked even itself on Saturday when it voted to approve a two-year moratorium on sales of AR-15 semiautomatic rifles, going far beyond the gun-related measures that Republican legislative leaders said they would consider.

Tellingly, though, that two-year moratorium lasted only 15 minutes.

It had been approved by a voice vote, and opponents quickly insisted on reconsidering it, this time with a roll call to formally record how each senator voted. Evidently that turned some of the ayes heard by the Senate president into nays, because the proposal was defeated, 21 to 17.

The moratorium episode — the closest that Florida’s Democratic gun-control proponents have come to success after a Feb. 14 shooting rampage, at a high school in Parkland, left 17 people dead — illustrates why it is so difficult to pass firearm restrictions in the State Legislature: When it comes to backing a significant change, even a popular one, the votes just aren’t there.

Democrats are powerless in capital

In the rare Saturday session, the Senate debated a Republican-sponsored bill that would raise the minimum age to purchase a firearm to 21 from 18; mandate a three-day waiting period for most gun purchases; ban bump stocks, which enable semiautomatic rifles to fire much faster; and set up a voluntary program to arm trained schoolteachers and pay them a stipend to participate.