The Republican chairman of the Senate Judiciary Committee said Ms Miers needed, at the very least, a "crash course in constitutional law".
The controversy is also bolstering a perception of rampant cronyism in government ranks - at a time when some of the president's appointees and closest allies are either under indictment or at risk of being indicted in the very near future.
Ms Miers was President Bush's personal lawyer before coming to work as a White House counsel - a background that has unexpectedly triggered disdain rather than confidence in the president's own party.
John Tierney, writing in the New York Times, said scornfully that the president might just as well have nominated Judge Judy, star of a a daytime small-claims court television series.
Staunch senate conservatives such as Sam Brownback of Kansas, an ardent anti-abortion campaigner, have said they may well vote against her. Arlen Specter, the more moderate chair of the Senate Judiciary Committee, also sounded a sceptical note when asked about her on a Sunday morning television chat show.
"When you deal in constitutional law, you're dealing in some very esoteric, complicated subjects that require a great deal of background," he said. "The jurisprudence is very complicated, and I will be pressing her very hard on these issues."
Reasons vary for the dismay at Ms Miers. Although she is an evangelical Christian, many conservatives are furious the president did not pick a high-profile conservative legal scholar with an openly ideological judicial bent. Others appear genuinely aggrieved at her apparent lack of qualifications for the job.Reuse content