The fight for America begins in N.J. As our hottest congressional race goes, so may go the nation.

On the surface, the fevered race in New Jersey’s 7th Congressional District looks like a natural rematch between candidates who fought to a near-draw two years ago. But to a politically split America slogging through a tough election year, the contest pitting Republican Tom Kean Jr. against incumbent Democrat Tom Malinowski is much more than that. What happens in New Jersey’s most competitive race could very well determine which party controls the U.S. House of Representatives at President Joe Biden’s midterm, and not simply because this one seat could stay Democrat or flip to Republican. Like...