LOUISVILLE — Donald Trump – who just a few years ago praised President Obama’s appeal for stronger gun control after the mass shooting in Newtown, Connecticut – was endorsed and embraced by the National Rifle Association on Friday, completing his rapid transformation into a fierce pro-gun advocate.

Instead of detailing his own positions on gun rights issues at a political forum attended by thousands of NRA members, Trump told the crowd that Democratic front-runner Hillary Clinton would “abolish the Second Amendment” and then release violent criminals from prison, not caring that innocent citizens would be unable to protect themselves.

“Hillary wants to disarm vulnerable Americans in high-crime neighborhoods,” Trump said. “Whether it’s a young single mom in Florida or a grandmother in Ohio, Hillary wants them to be defenseless, wants to take away any chance they have of survival. … And that’s why we’re going to call her ‘Heartless Hillary.’ ”

Clinton fired back on Twitter: “You’re wrong, realDonaldTrump. We can uphold Second Amendment rights while preventing senseless gun violence.”

Maya Harris, Clinton’s senior policy adviser, said Trump’s remarks are “conspiracy theories” that “distract from his radical and dangerous ideas.”

Gun control has become a dominant issue in the presidential race, though neither party has yet to formally install its nominee. This week highlighted the stark differences between Trump and Clinton, who will be the featured speaker at a Saturday fundraising dinner for a memorial foundation honoring Trayvon Martin, the unarmed Florida teenager shot and killed by a neighbor in 2012.

Clinton, who has criticized Democratic challenger Bernie Sanders for not being strong enough on gun control, plans to expand that focus in the general election. She has criticized Trump for being cavalier about gun safety and warned in a Twitter message last week that Trump would force schools to allow firearms in classrooms because he no longer wants schools to be gun-free zones.

Clinton has never called for the repeal of the Second Amendment, and fact-checkers have discredited Trump’s assertion that she would abolish it. Instead, she has said she would narrow the loophole that allows easy purchases of firearms at gun shows or online. She also has pledged to seek legislation to end immunity from many lawsuits for gunmakers.

“The gun lobby is the most powerful lobby in Washington,” she said at a recent appearance in Hartford, Connecticut. “They have figured out how to really intimidate elected officials, at all levels, who basically stop thinking about this problem because they are too scared of the NRA.”

NRA leaders repeatedly warned their members Friday that if Clinton is elected, their individual freedoms will disappear and the Supreme Court will start limiting the rights of gun owners.

“You can kiss your guns goodbye,” said NRA chief executive Wayne LaPierre.