Ever wonder how Beltway insiders assess which congressional seats are potential flips, and therefore worth a cash infusion?  Since the late 1990s, a favorite tool for pros has been the Cook Political Report's PVI — the Partisan Voter Index. Today, Henry catches up with Dave Wasserman to look into how the PVI is calculated and to help us understand what numbers mean; they review earlier reports to understand how the country trended toward partisan gridlock over the years, and consider how Donald Trump's favorability numbers come Labor Day 2026 will influence which districts election committees will consider within reach (and which beleaguered incumbents will be wise to consider scorching earth).