Defenders of the Miers nomination seem to have shifted from saying that there's no point in criticizing it because confirmation is assured to saying that criticizing it is destructive because its withdrawal or defeat would cause large Republican losses next November. The shift in emphasis seems to suggest the nomination's increased vulnerability. Even if it doesn't, the electoral point is worth taking seriously. Looking back at the Bork debacle of 1987 won't settle the question, but may be worth doing. Conservatives were far more invested in the Bork nomination than they are in the Miers nomination. Bork was defeated, not withdrawn. And the president was further embarrassed when his next nomination had to be withdrawn, too. These events have had long-lasting negative effects. But their immediate electoral effects were not so large. Republicans lost one Senate seat, and kept the presidency, in 1988.
Conclusion: even if the nomination is in jeopardy, even if it is withdrawn or defeated, it won't cause the kind of electoral harm people like Hugh Hewitt are now trying to tout.
The only way that a Miers' withdrawal causes lasting electoral harm to the Republicans is if Bush nominates a moderate candidate. Naming a superior conservative candidate with intellectual heft and a known track record would undo any damage, IMHO.