PHILADELPHIA — Ronald Reagan was on the screen warning about the scourge of nuclear war. George H.W. Bush was featured on a video discussing the dangers global warming. A reference to John McCain triggered a standing ovation.

The penultimate day of the Democratic National Convention was mostly about party unity, as Vice President Joe Biden and President Obama made a closing pitch for Hillary Clinton and everyone in the coalition from the Michael Bloomberg center-left to the democratic socialist Bernie Sanders coalesced behind her.