Donald Trump and Hillary Clinton are engaged in their first full-blown Twitter war.
Trump started it, mocking President Barack Obama's endorsement of the presumptive Democratic nominee on Thursday.
"Obama just endorsed Crooked Hillary. He wants four more years of Obama_but nobody else does!" Trump tweeted.
Clinton's campaign responded with an epic troll: "Delete your account," her campaign replied.
The message marked a departure for the often cautious Clinton and quickly went viral, getting retweeted 130,000 times in about an hour. It was a campaign milestone: Clinton's most retweeted tweet.
"Delete your account" is a...