The big infrastructure deal President Biden and a group of senators from both parties announced Thursday is about much more than infrastructure. It may well be a test of whether bipartisanship can survive in today’s Washington on any big subject.

After all, if bipartisanship can’t be achieved on infrastructure—the motherhood-and-apple-pie issue of our times, where every lawmaker gets to send some federal dollars back home for projects their constituents can see and use—where can it happen?

That doesn’t mean the $1.2 trillion deal—which would represent one of the biggest investments ever...