Harris and Walz Make Their National Entrance Before Upbeat Democrats

Vice President Kamala Harris finished her two-week sprint to find a running mate by formally introducing Gov. Tim Walz of Minnesota to the Democratic Party and the nation during a jubilant rally on Tuesday evening in Philadelphia.

Ms. Harris hailed Mr. Walz, an affable former high school football coach whose elevation to the national ticket seemed hard to imagine when President Biden left the race, as the governing partner she had searched for.

“Tim Walz was the kind of teacher and mentor that every child in America dreams of having and that every kid deserves,” Ms. Harris said. “The kind of coach — because he’s the kind of person — who makes people feel like they belong and then inspires them to dream big. And that’s the kind of vice president he will be. And that’s the kind of vice president America deserves.”

The presentation of the Harris-Walz ticket before an adoring crowd, an estimated 12,000 people between the arena and an overflow room, began the next chapter in one of the most turbulent periods in modern American politics.

Just 40 days ago, President Biden was preparing to debate former President Donald J. Trump in what his campaign described as the kickoff to the general election. But Mr. Biden delivered a performance so alarming that his party exploded in revolt, ultimately pushing him out of the race just over two weeks ago.

In short order, Ms. Harris’s emergence as the nominee has transformed what had been a Democratic Party depressed by the prospect of scrounging up votes for an unpopular 81-year-old candidate. Instead the party has revived itself behind Ms. Harris, who has injected new hope into her party heading into the highly competitive homestretch of the election.