(CNN) -- Goodwin Liu, a California law professor nominated by President Barack Obama for the 9th U.S. Circuit Court of Appeals, asked Thursday for his name to be withdrawn after Senate Republicans had invoked a rarely used filibuster to block a final floor vote.
"With no possibility of an up-or-down vote on the horizon, my family and I have decided that it is time for us to regain the ability to make plans for the future," Liu said in a letter to Obama. The letter was provided to CNN by a source at the University of California Law School, where Liu teaches.
The letter also cited a need for judges in the 9th Circuit, adding that "it is now clear that continuing my nomination will not address that need any time soon."
There was no immediate White House response to Liu's request.
Republican Sen. Charles Grassley of Iowa issued a statement Wednesday that said Liu had requested the withdrawal of his nomination, which was opposed by conservatives who said Liu was a partisan ideologue.
"I hope the president accepts Mr. Liu's request so we can finally move forward with a consensus nominee who reflects the mainstream of American views, respects the rule of law and the Constitution, and has an appropriate judicial temperament," Grassley said.
The liberal advocacy group People for the American Way also said Liu had asked for his nomination to be withdrawn. It accused Republicans of smearing Liu's reputation to score political points.
"Goodwin Liu would have made a superb jurist," the group's Marge Baker said in a statement. "He is highly respected by legal luminaries across the political spectrum and has shown a keen understanding of the protections that the Constitution grants all Americans. As an Asian American and the child of immigrants, he would also have added some much-needed diversity to the federal bench.
According to Baker, Republican senators ignored their own past vows to never filibuster a judicial nominee.
Last week, a cloture maneuver to end weeks of delays over the nomination failed when Democrats could not secure the necessary 60 votes to end debate and move to a final vote.
Liu became a political lightning rod over his liberal views and testimony given at confirmation hearings last year. Lawmakers on both sides traded barbs over his qualifications and his past statements on a variety of hot-button topics such as same-sex marriage and health care reform.
If confirmed, Liu would have become only the second Asian-American currently on the nation's federal appeals courts, the level just below the Supreme Court. Obama nominated him in February 2010.
The fight also was the latest test case over the political and ideological battle over judges, and whether Liu represents the "extraordinary circumstances" to justify a filibuster.
A bipartisan group of senators -- called the Gang of 14 -- reached a 2005 compromise agreement during the Bush years to prevent divisive filibuster tactics some have labeled the "nuclear" option. Nominees then and now were to be given a floor vote except under "extraordinary circumstances." Some conservatives say Liu fits that category.
As of last week there were 87 vacancies in the 857 federal district and appeals court judgeships, amounting to about 10%. Just 74 names have been currently put forth by Obama in the new Congress, many of them renominated -- but never confirmed -- from the past two years. Twenty-four candidates have received confirmation since January. The administrative office of the U.S. courts predicts at least 23 more vacancies this year.
Republicans had been criticized for delaying floor votes on many nominees in the president's first two years in office, but the White House, too, has come under fire for not moving quickly to fill growing bench vacancies. The president's two Supreme Court choices -- Sonia Sotomayor and Elena Kagan -- received relatively swift consideration.
Some moderates from both parties have long lamented threats of delays and filibuster attempts of most presidential appointments. They say ongoing unfilled vacancies have created a crisis in many federal courts, with bulging dockets being handled by too few judges. The circuit seat Liu would fill has been declared a "judicial vacancy" that the court says requires urgent consideration.
During separate testimony this past March and last year, the 40-year-old Liu apologized for omitting 117 items from a committee questionnaire on his background. The items were eventually submitted.
Republicans and other conservatives had questioned whether Liu was purposely withholding certain information on his background. Republicans said the material included statements on affirmative action and the effect that Obama's 2008 presidential win would have on the Supreme Court.
Opponents say he lacks prior experience as a judge or practicing attorney, and has spent most of his career in academia.
Democrats strongly defend Liu's record, saying opponents are unfairly characterizing his words and qualifications. He had assured lawmakers that despite some provocative statements he made as a law professor, he would act impartially as a judge.
"My personal beliefs have no role in the act of judging," he said. As an example, he noted, "I would have no difficulty or objection of any sort to enforcing the law as written in enforcing the death penalty."
Liu's supporters point to his years of scholarship, and especially his personal background. He was born to Taiwanese immigrant parents, attended public schools, then Yale Law School and was a Rhodes scholar. He later clerked at the Supreme Court for Justice Ruth Bader Ginsburg.
Republicans have made much of Liu's statements in support of same-sex marriage and affirmative action. A recent book he co-authored supports the idea of the "living" Constitution, which conservatives have long disdained. Liu said judges should interpret the Constitution "in light of the concerns, conditions and evolving norms of society," which many on the right deem a playbook for activist liberal judges.
Liu also openly opposed President George Bush's 2005 nominations of Chief Justice John Roberts and Justice Samuel Alito. Sen. Jon Kyl, R-Arizona, told Liu his nationally televised remarks during Alito's Senate hearing were out of line.
At that time Liu said, "Judge Alito's record envisions an America where police may shoot and kill an unarmed boy to stop him from running away with a stolen purse; where a black man may be sentenced to death by an all-white jury for killing a white man... this is not the America we know. Nor is it the America we aspire to be."
"This calls into question your judicial temperament," said Kyl at Liu's own hearing. "I see it as very vicious, and emotionally and racially charged, very intemperate and to me it calls into question your ability to approach and characterize people's positions in a fair and judicious way."
The 9th Circuit on which Liu would have sat is by far the largest appeals court in the United States and includes cases arising from the states of California, Washington, Oregon, Hawaii, Alaska, Nevada, Arizona, Idaho, Montana, and the Pacific territories. It is also considered the most liberal federal appeals bench, with 16 full-time judges named by Democratic presidents and 10 by Republicans.
Most of the cases accepted by the Supreme Court come from the 9th Circuit, a sign in part that the conservative majority on the high court has concerns with the appeals court's rulings.
CNN's Bill Mears and Dana Bash contributed to this story.