President Barack Obama's pick to sit on the D.C. Circuit Court of Appeals became the latest judicial nominee to face opposition from Republican senators, who voted Monday to maintain their filibuster of her confirmation.

The Senate voted 54-45 to end debate on the Caitlin J. Halligan's confirmation to the appellate court, far from the 60 votes needed to break a GOP filibuster. The vote fell mainly on party lines with one Republican, Sen. Lisa Murkowski of Alaska, siding with Democrats.

Halligan was nominated in September 2010 to a judicial seat that U.S. Supreme Court Chief Justice John Roberts had held before joining the high court. She was New York's solicitor general, the state's top appellate attorney, until 2006 and a partner at Weil Gotshal & Manges.

This is the second time this Congress one of Obama's judicial nominees faced a Republican blockade. This year, GOP senators successfully filibustered Obama's pick for the Ninth Circuit Court of Appeals, University of California Law, Berkley School of Law professor Goodwin Liu, who withdrew his nomination in May. California Gov. Jerry Brown, a Democrat, later offered him a spot on the state's Supreme Court.

A Republican filibuster of Halligan's confirmation is notable because of the D.C. Circuit's reputation as a bench for future U.S. Supreme Court justices and the second most significant court in the country. Judges in that court often hear prominent cases about federal law and regulation.

The new standard applied by Senate Republicans to nominations to the D.C. Circuit will make it nearly impossible for nominees of any president to be confirmed to this important court, Sen. Patrick Leahy, a Vermont Democrat who chairs the Senate Judiciary Committee, said Tuesday. Ms. Halligan is the kind of nominee we should all welcome to public service.

Sen. Chuck Grassley, the top Republican on the Senate Judiciary Committee, has said that nominations to this appeals court deserve special scrutiny. Grassley of Iowa has also pointed out the failure of President George W. Bush's nominees to get confirmed when Democrats controlled the Senate.

Grassley on the Senate floor Tuesday denounced Halligan's activist record, specifically her legal work in a gun control case and her participation in a New York City Bar Association report critical of the Bush's administration's detainee policies.

As New York's chief appeals lawyer, Halligan had a role in the state's lawsuit against gun manufacturers seeking to hold them liable for crimes committed with illegal handguns. She also filed an friend-of-the-court brief on behalf of New York State in favor of New York City's legal challenge to a federal law providing legal cover for gun makers.

Those lawsuits are prime example of how activists for the far left try to use the courts to effect social policy changes that they are somehow unable or unwilling to fight to achieve through the ballot box, Grassley said Tuesday. That is why I believe those lawsuits represent--not only bad policy--but more broadly an activist approach to the law.

Sen. Chuck Schumer, the No. 3 Senate Democrat from New York, said Halligan, who left private practice to become general counsel to the prominent Manhattan district attorney's office, deserves an up-or-down vote in the Senate.

He also suggested that Republicans seem want Obama to pick a judicial conservative, rather than allowing a nominee qualified attorney and a moderate with extensive government service.

The only arguments against Caitlin Halligan are gotcha arguments, Schumer said on the Senate floor, that simply take little snippets of what she did in past law practice--representing clients not her own views--and say 'gotcha.'

Schumer said a GOP filibuster of Halligan would have lasting consequences for the Gang of 14, a bipartisan group of senators who agreed in 2005 to only filibusters judicial nominees in extraordinary circumstances.

If this body cannot invoke cloture on her nomination today, Schumer said, the Gang of 14 agreement, it would seem to me, would be violated.