Gov. Tim Walz of Minnesota, a former schoolteacher who was first elected to Congress in 2006, will be Vice President Kamala Harris’s running mate, she announced this morning, ending several days of speculation.

The choice will very likely shine a light on the state of Minnesota, home to areas like “climate-proof Duluth,” which has seen a flood of new residents fleeing climate change over the last few years.

But Minnesota is also home of the one of the most remarkable transitions to clean energy in the country. As Coral Davenport put it, over his two terms as governor, Walz “has quietly emerged as one of the nation’s most forceful advocates for tackling climate change.”

As you think about vice-presidential choices, let me remind you why they can matter.

First, of course, there’s the chance a vice president could become president one day, as 15 vice presidents have.

When it comes to the presidential campaign, though, what matters is not just whether a vice-presidential pick can deliver voters in their own state or in their own constituencies. It’s what a running mate tells voters about what a presidential candidate values. As Kyle Kopko, a co-author of the book “Do Running Mates Matter?” told National Public Radio, many voters pay close attention to a V.P.’s experience and tend to value the ability to serve as president if needed.

So today I want to tell you a little bit about Minnesota’s transition away from coal and explain what that tells us about Walz’s experience and whether he can be an asset for Democrats.