Republicans and the Trump campaign — facing severe polling, staff and advertising disadvantages — might be tempted to point to party voter registration trends as a sign of life and evidence of an underrated ground effort. On Monday, a Politico analysis concluded that “at least one ray of hope for a turnaround” is that Republicans are “winning [the] registration race” in the key states of Florida, Pennsylvania, North Carolina and Iowa.It’s true that Democrats’ edge in voter registration has shrunk in those states since 2012, but much like the Trump camp’s claims of July fundraising success, there’s far more to this story.Party registration can often be a lagging, rather than leading, indicator.