While the skirmish lines are forming in Congress over President Obama’s nomination of a successor to the late Supreme Court Justice Antonin Scalia – the president first will have to make his choice known before the battle can be joined.

Though Obama had not been expecting to make a Supreme Court nomination in the final months of his second term, Scalia’s death triggers a rigorous selection process that begins with an informal list of nominees this administration -- and those before it -- keep in the event of a sudden vacancy. Serious vetting only begins, however, when a vacancy occurs or is announced.

And Obama will have plenty of names from which to choose. While not an official “short list,” the following list of potential nominees is based on past nominations and discussions with sources, including government officials involved in the selections of Justices Sonia Sotomayor and Elena Kagan:

Loretta Lynch, attorney general

The North Carolina native became the nation’s top law enforcement officer last year, after a bitter confirmation fight in the Senate. She served two stints as the U.S. attorney for the Eastern District of New York, earning a reputation as a tough prosecutor in several high-profile financial and terrorism-related cases. Most recently in the AG role, she filed a civil rights lawsuit against the Ferguson, Mo., Police Department over what she called its unconstitutional violation of the rights of the largely minority community. If successfully nominated, the daughter of a Baptist minister and a school librarian would be the first African-American woman on the high court.

Judge Patricia Millett, U.S. Court of Appeals for the District of Columbia Circuit     

 

Millett was named in 2013 to a bench considered a stepping stone to the high court -- where four current justices once served. Formerly a private Washington-based appellate attorney -- Obama called her "one of the nation's finest"-- who also had more than a decade of experience in the U.S. Solicitor General's office, Millett argued 32 cases before the Supreme Court, the second-most ever for a female lawyer. Sources of both ideological stripes call her fair-minded, no-nonsense and non-ideological.

Judge Sri Srinivasan, U.S. Court of Appeals for the District of Columbia Circuit   

Srinivasan was named to the court in 2013, months before Millett joined him. The son of Indian immigrants – who was born in India and raised in Kansas -- Padmanabhan Srikanth Srinivasan was the principal deputy solicitor general at the Justice Department, and argued more than two dozen cases before the Supreme Court. He would be the high court's first Asian-American. Known as low-key, practical and non-ideological, he may not excite many progressives, or give conservatives much to dislike.

Judge Paul Watford, 9th Circuit U.S. Court of Appeals

Watford was named to the appeals court in 2012. He clerked for conservative-libertarian federal Judge Alex Kozinski on the 9th Circuit, and later for liberal Justice Ruth Bader Ginsburg. Supporters call the Orange County, Calif., native an ideological moderate, which may not sit well with progressives seeking a stronger liberal voice.

Judge Jacqueline Hong-Ngoc Nguyen, 9th Circuit U.S. Court of Appeals

The Vietnam-born Nguyen was named to the court in 2012 after two years as a federal district court judge. She, too, would make history as the high court's first Asian-American justice. She is already the first Asian-American woman to sit a on a federal appeals court and is a former state judge, federal prosecutor and private attorney. She moved with her family to the U.S. when she was 10, just after the fall of then-South Vietnam to the Communists. 

Kamala Harris, California attorney general 

Harris was elected to her current job in 2010. Harris is a former San Francisco district attorney and author of "Smart on Crime." Her political savvy, ethnic background (part-African-American, part-Asian-American), law enforcement credentials and early support of Obama's candidacy make her a favorite for any high court vacancy.

Kathryn Ruemmler, former Obama White House Counsel

Ruemmler left her government position for private practice in spring 2014. She most famously helped lead the prosecution in the Enron fraud case in 2006. She earned high praise in the White House for helping spearhead the legal defense of Obama’s health care overhaul law. She also supervised the vetting for the Kagan and Sotomayor high court nominations, though she has no judicial experience.

Judge Jane Kelly, 8th Circuit U.S. Court of Appeals

Kelly is only the second woman to serve on the St. Louis-based court, appointed in 2013. She spent most of her legal career as a federal public defender in Iowa. One of her biggest fans is fellow Iowan Republican Sen. Charles Grassley, chairman of the Senate Judiciary Committee.

Judge David Barron, 1st Circuit U.S. Court of Appeals

Confirmed in May 2014, Barron formerly served as acting assistant attorney general in Obama administration, then went to Harvard Law School as a professor. He clerked for Justice John Paul Stevens.

Judge Diane Wood, 7th Circuit U.S. Court of Appeals  

Wood has sat on the bench since 1995. Twice a finalist for the high court vacancies in 2009 and 2010, she is considered a mainstream liberal and well-regarded by many legal analysts as a strong, articulate judge. She served in both the Reagan and Clinton Justice Departments.

Judge Merrick Garland, D.C. Circuit U.S. Court of Appeals

Garland was a finalist for the high court seats that went to Sotomayor and Kagan, and is a possible compromise choice, considered a relative judicial moderate on the high-profile appeals court. Four current justices came directly from the D.C Circuit. Garland was a former associate deputy attorney general and supervised the criminal prosecution of the 1995 Oklahoma City bombing. His perceived "moderate" views may not sit well with some liberals.

While Obama says he plans to nominate a Scalia successor, Republicans in the Senate are threatening to hold up the confirmation – in hopes that a Republican president will be able to make the selection next year. If the decision does fall to a Republican president, the following are a few possibilities:

Paul Clement, former U.S. solicitor general

Clement is considered by many one of the best lawyers of his generation. The Wisconsin native went to Harvard Law School and later clerked for Justice Scalia. He served as solicitor general under President George W. Bush and earned raves for his persuasive, conversational style at oral arguments before the justices. Now as a private attorney, he has become the go-to guy among conservatives to lead appeals over a variety of hot-button issues: health care reform, same-sex marriage, immigration enforcement and gun rights.

Judge Brett Kavanaugh, D.C. Circuit U.S. Court of Appeals

Kavanaugh began his job May 2006 in a court that has seen several of its former members make the jump to the Supreme Court. A former top official in the George W. Bush White House, his nomination to the prestigious D.C. circuit was held up for three years by Democrats who accused him of misleading over whether he helped formulate policy on the detention and questioning of accused terrorists held overseas. He is considered one of the brightest young conservative legal minds.

Judge Diane Sykes, 7th Circuit U.S. Court of Appeals

Sykes is a former private lawyer, county judge and justice on the Wisconsin Supreme Court. She is a Federalist Society member, and her profile has been increasing among many conservatives.

Sen. Mike Lee, Republican from Utah

The rising GOP star may have the best credentials of any lawmaker to be a justice. Lee is a former appellate and constitutional lawyer, both in Utah and Washington, who twice clerked for Justice Samuel Alito, on both the federal appeals and later Supreme Court.