The election Tuesday to replace 35-year GOP congressman Tom Petri of Fond du Lac may be Wisconsin’s most unusual U.S. House race in decades. That’s because of the extraordinary rift between Petri and the candidate his own party has nominated to replace him, state lawmaker Glenn Grothman. Grothman decided last April to run against Petri. It’s the kind of serious primary challenge that almost never happens in a Wisconsin congressional race. He continued to criticize Petri after Petri announced his retirement, saying he’d be insulted if he went to Washington and people thought he was “just like Tom Petri.” And...