Barack Obama accused Donald Trump of treating the US presidency like “one more reality show”, in a withering speech to the Democratic convention.
The former US president said his Republican successor “hasn’t grown into the job because he can’t”.
At the White House, Mr Trump hit back that he was only elected because of the “horror” Mr Obama left Americans.
On the third night of the Democratic conference, Kamala Harris accepted the vice-presidential nomination.
The grand finale of the four-night convention will see Democratic presidential nominee, Joe Biden, deliver a speech on Thursday.
The Biden-Harris ticket will challenge President Trump and his Vice-President, Mike Pence, for the White House in the election on November 3.
The coronavirus pandemic has forced Democrats to abandon the cheering throngs and razzmatazz that are the hallmarks of the quadrennial party convention in favour of a virtual event of pre-recorded and live speeches.
On Wednesday night, Mr Obama unleashed possibly his most scathing attack yet about Mr Trump, speaking live from the Museum of the American Revolution in Philadelphia.
He said, “He [Mr Trump] has shown no interest in putting in the work. No interest in finding common ground.
“No interest in using the awesome power of his office to help anyone but himself and his friends.
“No interest in treating the presidency as anything but one more reality show that he can use to get the attention he craves.”
He said the consequences of the Trump presidency have been “our worst impulses unleashed, our proud reputation around the world badly diminished, and our democratic institutions threatened like never before.”
The former president lamented “the circus of it all, the meanness and the lies and the conspiracy theories.”
“Do not let them take away your power,” he implored American voters. “Do not let them take away your democracy.”
Mr Obama encouraged voters to elect his former vice-president, Mr Biden, in 76 days’ time – praising him as “my friend” and “a brother”.
Trump, however, promptly fired back describing Obama as an “ineffective” and “terrible” leader.
“I see the horror that he’s left us, the stupidity of the transactions that he made,” Trump said.
“President Obama did not do a good job. The reason I’m here is because of President Obama and Joe Biden,” he said.
