Four years after his son Joaquin was shot and killed at Marjory Stoneman Douglas High School in Broward County, Manuel Oliver’s pain is still raw. Right or wrong, he took his personal fight to the White House lawn on Monday. On national television, Oliver rudely interrupted President Joe Biden during an event meant to celebrate what many consider a bipartisan, but watered-down, law to reduce gun violence. “Today is many things. It’s proof that despite the naysayers, we can make meaningful progress in dealing with gun violence. Because make no mistake — ” Biden was saying when Oliver jumped up …