Why did Harris pick Walz as her running mate?

Ciaran Jenkins: The race for the White House has moved up a gear – with both the Trump and Harris campaigns holding rival events in the key battleground states of Michigan and Wisconsin today. Momentum – for the moment at least – seems to be with Harris, who unveiled her running mate Tim Walz last night. For many Americans, it was the first chance to see Walz – the relatively low-profile Minnesota governor – up close.