Five and a half weeks after House Republicans passed their budget, Democrats and liberal pundits have decided it is political kryptonite that will fatally weaken the GOP.

Their evidence is Tuesday's special election in New York's 26th district, where Democrat Kathy Hochul defeated Republican Jane Corwin for a vacant congressional seat. This is not just any congressional district, but one carried by George W. Bush and John McCain in the last two presidential elections, and one...