It’s Harris’ time to convince voters that she can be the 47th president

Her speech at the Democratic National Convention on Thursday night will represent her most exacting test yet in a dizzying month that rocketed her to the threshold of an historic presidency that could reshape American politics.

The vice president will offer the country a new beginning and a chance to move to a different place — beyond the prolonged funk brewed by years of Donald Trump’s dark rhetoric and public exhaustion after a once-in-a-century pandemic and consequent and punishing high prices.

More broadly, she’s proposing to restore the elusive lightness and optimism to...