Shortly after his successor in the White House addressed the nation on Wednesday's deadly mass shooting at a south Florida high school, former President Barack Obama made his first public comments on the rampage that left 17 people dead.Obama, who spoke to the nation multiple times after tragedies, made another call for some form of gun control in an afternoon tweet on the shooting at Parkland's Marjory Stoneman Douglas High School."We are grieving with Parkland," he wrote. "But we are not powerless. Caring for our kids is our first job. And until we can honestly say that we're doing enough to keep them safe from harm, including long overdue, common-sense gun safety laws that most Americans want, then we have to change."Before Obama's short message, President Donald Trump gave an address from the White House focused on tackling mental health issues. Following a 2012 shooting at Sandy Hook Elementary School in Connecticut that left 20 children and six adults dead, Obama announced that then-Vice President Joe Biden would lead an effort to develop a policy toward reducing gun violence. It did not result in any notable legislation, however.On Thursday, Biden again implored Congress to take action:"I am at a loss for what more to say. I grieve with the families in Parkland today. I grieve with the families across the country who have suffered loss due to gun violence. Congress has a moral obligation to take action and spare more families from this violence."