Clinton is expected to formally accept the Democratic nomination on Thursday, just a week after business mogul Donald Trump became the Republican nominee.
Obama said she believed Trump is unfit to hold the highest office in the land because of his temper.
"When you have the nuclear codes at your fingertips and the military in your hands, you can't make snap decisions," she said, adding the presidency "can't be boiled down to 140 characters."
Obama is no stranger to the Democratic National Convention's spotlight, having delivered speeches in both the 2008 and 2012 conventions.
I totally agree with her..Well said !!!