First lady Michelle Obama emerged from the first day of the Democratic Convention as an unexpected ace in the hole for Hillary Clinton, as many Democratic observers said she bridged the party divide like no other on Monday, and successfully made the case for a former rival she once described as unfit for office.

After a day full of party divisions and rancor over leaked Democratic National Committee emails and jeers by Bernie Sanders’ supporters, Democratic party operatives and current White House staffers were left cheering the first lady’s prime-time speech. Some even hailed it as one of the greatest Democratic convention speeches in history.