Who is Caitlin Halligan?

A 46-year-old lawyer and litigator, she is at the center of a Senate showdown set for Wednesday over President Obama’s judicial nominations. This is Halligan’s second time before the Senate—her initial appointment to the D.C. Circuit Court ended in a Republican-led filibuster in 2011. Now she’s back, reappointed by the president and the symbol of a new White House push to get Obama’s judicial picks in place—or failing that, to raise the political cost to Republican senators who block qualified appointees to score ideological points.

Almost half of Obama’s judicial nominations die a quiet death with little publicity or public awareness of the toll it takes on the nominees who wait months and sometimes years for the Senate to grant them a vote. Halligan was first proposed for the D.C. court almost two and a half years ago. A graduate of Princeton and Georgetown Law, she is rated “unanimously well qualified” by the American Bar Association and is general counsel at the Manhattan district attorney’s office.

“She has a stellar academic background, but these fights don’t typically come down to qualifications,” says Sarah Binder, a professor of political science at George Washington University and a senior fellow at the Brookings Institution. “They come down to policy, particularly social policy on the appellate court,” which divides along party lines.

Democrats need five Republican votes to reach 60 and overcome a GOP filibuster that would again block Halligan’s nomination. Republican Lindsey Graham voted “present” on her nomination in the Judiciary Committee last month, a change from his previous vote of no, offering what a White House aide calls “a glimmer of hope.”

When the roll call is taken Wednesday, the critically deciding votes will likely be cast by Republicans Graham, John McCain, and Kelly Ayotte. “Those three have indicated they’re not in the ‘no’ column,” says Nan Aron, president of the liberal Alliance for Justice, offering some hope that they will allow the nomination to proceed to a vote.

Another Republican, Lisa Murkowski, did not block Halligan’s nomination in 2011 and together with two possible GOP colleagues, Susan Collins and Mark Kirk, might help break the filibuster. “It’s still an uphill fight,” says Aron, who believes the fight is less about Halligan and her credentials than it is about presidential power on the court most likely to review laws passed by Congress, along with executive actions and regulations. “They just don’t want to give the president another seat on the D.C. circuit,” says Aron.

The Committee for Justice, a conservative outside group, said in a statement: “Perhaps Democrats believe that their campaign for increased gun control makes Halligan look a little less extreme this time around. To the contrary, we suspect it has made GOP senators more sensitive to the Second Amendment records of judicial nominees who if confirmed, will determine the constitutionality of any new gun laws.” Calling Graham’s “pass” vote in committee last month an exception, the group is telling supporters that McCain, Collins, Kirk, and Lamar Alexander “could use some reminding about the importance of stopping Halligan.”

Brad Blakeman, who worked in the Bush White House and now teaches politics at Georgetown, says, “The problem in Washington is tit for tat and ‘you guys did it to us so we’re doing it to you.’” The GOP should end the filibuster, he says: “Every president should have broad latitude to name the people he or she wants. We have to get over it. Let the vote go forward.”

Given the small number of cases the Supreme Court takes, the D.C. circuit becomes the court of last resort, handing down rulings on the constitutionality of legislation that is challenged and the regulations that the federal government promulgates. It is also a stepping stone to the Supreme Court, the place where potential justices are groomed and observed. Among its notable alums are three current justices, Antonin Scalia, Clarence Thomas, and Ruth Bader Ginsburg.

There are four vacancies on the D.C. appellate court, out of 11 slots, so it will be difficult for the GOP to claim that the workload doesn’t justify filling the seat, as Republicans did when they filibustered Halligan in 2011, when the court had three vacancies. Democrats point out that Bush appointees were confirmed to the 10th and 11th seats on the court when Bush was president. Halligan would fill the eighth seat on the court. Republicans are clear about why they oppose her, highlighting cases that she worked on in the DA’s office, and before that as New York state solicitor general, as indications of how she might rule as a judge.

Republicans cite her advocacy for the state in a case involving abortion protesters. Another sticking point is a case in New York she brought against gun manufacturers. “If a zealous advocacy for your client as a lawyer bars you from the court, they’ll have to empty the bench,” says Matt Bennett, a lawyer and co-founder of Third Way, a moderate Democratic group.

“She is not the left’s answer to Miguel Estrada,” says a White House aide, conjuring up the 2001 fight over President Bush’s nomination of Estrada, a brilliant young conservative in the far-right Scalia mold whom Democrats repeatedly blocked from a seat on the D.C. court, fearing the seat would launch him to the Supreme Court. Halligan is “no lightning rod,” says the Obama aide, citing her conservative credentials from Republicans she has worked with and for, including an endorsement from Estrada, who practices law in Washington.

Blocking judges by running out the clock is a time-honored tradition when a president’s term is winding down. But Obama still has most of four years left, and Aron and others welcome what they see as a new assertiveness in getting his judicial nominations before the Senate and fighting for them. Win or lose Wednesday, the White House hopes to gain more visibility for these typically under-the-radar fights, making it perhaps a little less easy for Republican senators to escape unscathed when they hide behind the filibuster to protect their right flank.