Who came up with gun free zones, then?
Yeah, that's right, Joe Biden. A liberal. A leftist.
I present Exhibit A: The Gun Free School Zones Act of 1990, introduced by Biden and signed by George H.W. Bush.
Gun-Free School Zones Act of 1990 - Wikipedia
And Exhibit B: The overall success (or lack thereof) of the GFSZA. In the past 28 years, there have been 65 school shootings (not counting the one in Parkland, FL)
United States school shootings, 1990-present - Ballotpedia
My conclusion? These schools (including Marjory Stoneman Douglas High School) followed a plan introduced by a leftist, and judging from the number of lives lost since the GFSZA was enacted, I would consider this "plan from the left" an abysmal failure.
Your honor, I rest my case.