The presumptive Democrat presidential nominee employed a popular meme to rubbish Trump's attack on Obama's endorsement of her.
After the current President congratulated Clinton on "making history" by winning enough delegates to secure the nomination, Trump used his treasured Twitter account to post to his almost nine million followers:
But the post spurred Clinton to use a popular Internet meme to fire back at Trump, replying just five minutes later:
Some two hours after, Trump managed to assemble a comeback, quipping: "How long did it take your staff of 823 people to think that up?"
He also pointed to the controversy over Clinton's alleged deletion of thousands of emails.
Her tweet earned more than ten times the re-tweet's Trump's did, but prompted desperation from some, who feared the direction US politics seemed to be heading in.
Others made light-hearted fun of her post.
But not everyone was pleased at the tweet.
Trump hit out at Clinton late on Thursday night following the release of a video by President Obama in which he said: “I don’t think there’s ever been someone so qualified to hold this office.
The Democrat, who has been in office for almost eight years, added: “I want those of you who’ve been with me from the beginning of this incredible journey to be the first to know that I’m with her.”
Clinton is expected to battle against Donald Trump, the likely Republican Party nominee, in the upcoming US presidential election on November 8.
It came after US filmmaker Michael Moore admitted that he was "wrong" to think Trump would never stand a chance of being elected US President.
"I believe he can win in November," Moore said.
"I've learned my lesson - Trump can get elected and I'll do the math for you quickly. All he has to do is win the traditional, what we call 'red states', from Idaho and Utah to Georgia.
"Those states, then win the Rush Belt - four states. If he wins Michigan, Ohio, Pennsylvania and Wisconsin - and he's big there."