Timing of High Profile Shootings in the US

Here's the timing of high profile mass shootings in the US. See any pattern? Can anyone tell me what gun laws have been changed in the past as a result of these shootings? Either Federally or by state?

PARKLAND, Florida, February 14, 2018, 17 dead
AZTEC, New Mexico, Dec. 7, 2017, 3 dead
SUTHERLAND SPRINGS, Texas, November 5, 2017, 25 dead
LAS VEGAS, Nevada, October 1, 2017, 59 dead
CHARLOTTESVILLE, Virginia, August 12, 2017, 1 dead
ALEXANDRIA, Virginia, June 14, 2017, Scalise
FT LAUDERDALE, Florida, January 6, 2017, 6 dead
DALLAS, Texas, July 7, 2016, 6 dead
ORLANDO, Florida, June 12, 2016, 49 dead
SAN BERNARDINO, California, December 2, 2015, 14 dead
ROSEBURG, Oregon, Oct. 1, 2015, 9 dead
CHARLESTON, South Carolina, June 17, 2015, 9 dead

President Trump announces candidacy, June 16, 2015

NEWTOWN, Connecticut, Dec. 14, 2012, 26 dead
AURORA, Colorado, July 20, 2012, 12 dead
CHARDON, Ohio, Feb. 27, 2012, 3 dead
TUCSON, Arizona, January 8, 2011, Gabby Giffords

FORT HOOD, Texas, November 5, 2009, 14 dead
BINGHAMTON, New York, April 3, 2009, 14 dead
CARTHAGE, North Carolina, March 29, 2009, 8 dead

DEKALB, Illinois, Feb. 14, 2008, 5 dead
BLACKSBURG, Virginia, April 16, 2007, 32 dead

LITTLETON, Colorado, April 20, 1999, 13 dead