Mr Bush unveiled his choice at an early morning Oval Office appearance, with the 60-year old Ms Miers at his side. Ms Miers is a long-time friend and ally of the President, serving as his personal lawyer before coming to the White House in 2001 in the key job of staff secretary. She was then promoted to deputy chief of staff before becoming White House Counsel, the top lawyer to the President.
But the most salient point, from the perspective of the confirmation hearings likely to start at the end of this month or early next, is that although she is a lawyer, she has never served as a judge. She thus leaves no paper trail of rulings and opinions that would throw light on her views on vital issues likely to come before the court, including abortion, gay rights and church-state relations.
The prospect is disconcerting for all sides. But the initial reaction from Democrats was surprisingly positive indeed the party's Senate leader, Harry Reid, is said to have been among those who urged Mr Bush to look at Ms Miers.
"This was a good first day," said Charles Schumer, a New York Democrat on the Judiciary Committee, who voted against John Roberts, comfortably confirmed by the Senate as the country's 17th Chief Justice last week. But, he added, "we just don't know very much".
Those words could foreshadow a fierce tussle between Democrats and the White House over the release of White House documents that might give an indication of Ms Mier's thinking on sensitive topics. Ms O'Connor, whom she will replace, was often the crucial swing vote among the nine justices.
But conservatives are even more worried that Mr Bush weaker than at any time in his presidency has missed an opportunity to push the court to the right.
Introducing his nominee, Mr Bush said that she would not legislate from the bench and would strictly interpret the constitution language tailored to assure conservatives that Ms Miers was one of theirs.
William Kristol, editor of the conservative Weekly Standard magazine, said he was "disappointed, depressed and demoralised" by the appointment. It was "very hard to avoid the conclusion that President Bush flinched from a fight on constitutional philosophy," he said.
Charges of cronyism were rejected by the White House. Ms Miers "brings diverse and broad experience that will be very helpful" with the Court, a Bush spokesman said.
If their doubts become serious, Democrats could be tempted to mount a filibuster campaign against her. That in turn might trigger the so-called "nuclear option" by the Republican majority, changing the rules so that debate could be halted by a simple majority of the 100-seat Senate, rather than the super-majority of 60 currently required.Reuse content