At the outset of the campaign season, California Republicans held up the U.S. Senate contest as a marquee race for a newly energized, newly cohesive state GOP. Party leaders promised they would demonstrate that firing the Democratic governor last October was simply the start of an important revival for the long-sagging party. The answer came with a giant thud Tuesday night, in the form of a crushing, 21-point victory for incumbent Democrat Barbara Boxer and wins for Democrats in some key legislative and congressional races. Now Democrats and even some moderate Republicans say that the weak challenge against Boxer and...