Saturday's decision by Republican Dede Scozzafava to drop out of tomorrow's special Congressional election in upstate New York is a potentially big political moment that could help to return the GOP to first principles—or could lead to internecine ruin. Much will depend on how GOP leaders and conservative activists respond.

Picked by GOP elites without a primary and with a voting record to the left of many Albany Democrats, Ms. Scozzafava faced a revolt by local and national conservatives in favor of businessman Doug Hoffman, who was nominated on the Conservative Party line. The longtime GOP assemblywoman saw herself falling in the polls and yesterday endorsed Democratic lawyer Bill Owens, who could still win the GOP-leaning seat with a plurality.

The voter revolt...