Two weeks after becoming the Democratic nominee for president, Vice President Kamala Harris’s surge in enthusiasm and support has considerably narrowed the 2024 election. Last week in these pages, we wrote that while there was limited data available, Harris was clearly an improvement over President Biden. Now, new national and state-level polling suggests that assessment might be even more prescient, and points to an election that will be much closer than many had expected. Indeed, national polling underscores just how much the race has tightened. According to the 10 most recent public polls conducted after Biden’s withdrawal and aggregated by...