Bloomberg View

You can’t beat somebody with nobody. As political adages go, that one has proved durable and true. However, if America’s relentless march toward blue-state-red-state polarization continues, “nobody” may become an increasingly common option on voter ballots.

Four states lack a major-party competitor for current U.S. Senate races, the Smart Politics blog at the University of Minnesota’s Humphrey Institute of Public Policy reports. Democrats have yet to field a candidate in Alaska or Oklahoma, and Republicans have blank slates in Hawaii and Vermont. …

This lack of opposition reinforces the partisan divide. For many members of Congress, the threat of a primary opponent is more real than the prospect of a robust general-election challenge.

It’s bad enough that polarization squeezes competition out of a system that’s designed to encourage it. But if parties fail to field a candidate, especially in statewide races for U.S. Senate, the electorate is denied even the potential for genuine debate. It’s hard to challenge conventional wisdom, lazy assumptions or party dogma if there’s no one on the opposite side to make the case.

You don’t need to summon Britain’s finest hour or “Dewey Defeats Truman” to appreciate that democracy sometimes requires faith in the long shot. American political parties represent the whole of the nation. (When they fail to, the results are profoundly ugly.) They should field qualified candidates for every seat in the House of Representatives and, certainly, the Senate — and make sure those candidates have the resources to make their appeals to voters.