FORT LAUDERDALE - Florida state lawmakers were due to vote once more on Wednesday on a gun-safety package that would raise the legal age for buying rifles, impose a three-day waiting period on all firearms sales and allow the arming of some public school personnel.
The legislation, which narrowly cleared the state Senate on Monday, was spurred by the shooting deaths last month of 17 people at Marjory Stoneman Douglas High School in Parkland, Florida, and the lobbying campaign mounted by young survivors of the massacre.
The state House of Representatives rejected three dozen amendments to the bill on Tuesday, including a last-ditch bid to strip the legislation of any measures permitting school staff to carry guns to work.
The bill was scheduled to return to the House floor on Wednesday for what could be a final vote. Any amendments offered at that stage would require a two-thirds vote for approval.
If the bill passes the House unchanged, it would automatically become law within 15 days, unless vetoed or signed by the governor beforehand.
Swift action in the Republican-controlled Tallahassee statehouse, where the National Rifle Association has long held sway, signalled a possible turning point in the national debate between gun control advocates and proponents of firearms rights enshrined in the Second Amendment of the US Constitution.
The bill under consideration this week represented both a break with the NRA on gun sale restrictions and a partial acceptance of its proposition that the best defense against armed criminals is the presence of "good guys with guns."
To that end, the bill creates a program allowing local sheriffs to deputize school staff as volunteer armed "guardians," subject to special training, mental health and drug screening and a license to carry a concealed weapon.
Each school district would decide whether to opt into the program.
But classroom teachers are excluded as participants unless they meet one of three narrow criteria - they are Junior Reserve Officers Training Corps instructors, serve in the US military or are former police officers.
Otherwise, only non-teacher personnel are eligible, such as administrators, guidance counsellors, librarians and coaches.
The carve-out for teachers was aimed at winning support from Governor Rick Scott, a Republican and staunch NRA ally who nevertheless is opposed to arming teachers.
Many parents, law enforcement officials and legislators in both parties likewise object to allowing guns in the classroom.
US President Donald Trump has voiced support for arming teachers as a deterrent to gun violence in schools.
A spokeswoman for Scott has said he considered the bill a "step in the right direction" but had concerns with the proposed three-day waiting period for purchases of all firearms.
A three-day wait currently applies in Florida only to handgun sales.
Another key provision of the bill would raise the minimum legal age for all gun purchases in the state to 21.
The minimum age for handguns nationally is already 21. But a person can be as young as 18 to buy a rifle in Florida.
Nikolas Cruz, charged with killing 14 students and three adult educators in Parkland on 14 February was 18 years old when he legally purchased the semiautomatic AR-15-style assault rifle used in the massacre, police have said.
While state legislators voted against banning assault weapons outright in Florida, the bill would outlaw "bump stocks" that enable a semiautomatic weapon to be fired as if it were a fully automatic machine-gun.
The bill also makes it easier for police to temporarily seize guns from people involuntarily committed or deemed a danger to themselves or others by a court.
Authorities have said Cruz had a history of mental issues, numerous encounters with police and was expelled from Stoneman Douglas High School last year for disciplinary problems.
Law enforcement agencies also acknowledged receiving multiple warnings about his potential for violence before the shooting.