Democrats let loose with roars Wednesday evening for the version of Minnesota Gov. Tim Walz that they have come to know over the past month: The new favorite mascot of progressives, the guy who lands a stinging partisan punch, the flannel-shirted happy warrior from the heartland. Listening to his lines, and the thundering applause they summoned, my mind went back to a different version of Walz I experienced not very long ago. It was the summer of 2020 — in the middle of the pandemic, just...