First, recall that at the conclusion of the Roberts hearings, Republicans gleefully pointed out that 22 Democrats, led by Senator Charles Schumer (D-NY), had voted against a clearly qualified and truly outstanding nominee at the behest of far-left special interest groups. Forcing the President to withdraw the Miers nomination likewise would open Republicans to charges that the President is toeing a line laid down by a highly energized and vocal interest within his own party. That, in turn, would position the Democrats to argue, wrongly but credibly, that judicial selections are being dictated by an elite cadre of "scary extremists." Hardly the impression that Republicans want lingering in a voter’s mind on Election Day.
Moreover, for the past five years, Republicans have, quite rightly, faulted Senate liberals for imposing an ideological litmus test on judicial nominees. Noting that Ruth Bader Ginsburg was confirmed with a vote of 96-3 and that Antonin Scalia ascended the court on a 98-0 vote, Republicans have repeatedly invoked the days when nominees were evaluated on their qualifications and competence – not on their ideology. By opposing Ms. Miers on the basis of their worst (but yet unproven) fears about her political preferences or philosophy, conservative critics lend credibility to the argument that both judging itself and the evaluation of judicial nominations are irreducibly political exercises.
Finally, a premature withdrawal of the Miers nomination would create other political problems. Outside-the-beltway Republicans, along with evangelical leaders like Dr. James Dobson and Richard Land, look favorably on the Miers nomination. Anti-Miers rationales – ranging from "we're afraid she's not an originalist" to "she's not the best qualified candidate" to "the President should have picked someone else" – simply don't resonate with a significant portion of the Republican base. They see nothing amiss with Ms. Miers' credentials, and are inclined to trust the President's judgment on the nominee given his record on appellate judges, tax cuts, the war on terror and social security reform. Seeking to sabotage the Miers nomination before a hearing creates the misimpression within the party (and without) that some prominent Republicans disdain the achievements of a woman who is, at the very least, an accomplished legal practitioner and trailblazer.
I don't know whether the President expected the criticism he has received especially from fellow conservatives over this nomination. He's not been one to back down from a fight before. My guess is he'll run the risk of having the Senate deny Ms. Miers a seat on the Court before he would withdraw the nomination. Given the political fallout that could occur if he did withdraw the nomination it's probably better to go ahead and fight this one out even if it means losing the battle.