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Loretta Lynch was confirmed Thursday as attorney general, the first black woman in American history to hold the country’s top law enforcement post.

The Senate approved Lynch, a federal prosecutor from New York, on a 56-43 vote after an unusually lengthy confirmation delay. President Barack Obama nominated Lynch as the successor to Eric Holder in November.

Lynch's path to becoming the first African American woman to serve as attorney general was fraught with partisan bickering — fighting that continued on Thursday.

Obama said the Justice Department would benefit from Lynch’s experience as a “a tough, independent, and well-respected prosecutor.”

"Loretta has spent her life fighting for the fair and equal justice that is the foundation of our democracy,” the president said in a statement on Thursday. “As head of the Justice Department, she will oversee a vast portfolio of cases, including counterterrorism and voting rights; public corruption and white-collar crime; judicial recommendations and policy reviews - all of which matter to the lives of every American, and shape the story of our country."

Holder said he was pleased the Senate recognized "her clear qualifications."

"I have known and worked closely with Loretta for many years, and I know that she will continue the vital work that this Administration has set in motion and leave her own innovative mark on the Department in which we have both been privileged to serve,” Holder said in a statement. "I am confident that Loretta will be an outstanding Attorney General, a dedicated guardian of the Constitution, and a devoted champion of all those whom the law protects and empowers."

But Lynch faced staunch Republican objection to her support of the president’s use of executive action on immigration policies — including the deferred deportation of up to 5 million undocumented immigrants.

Sen. Ted Cruz, R-Texas, said Lynch will disregard the Constitution if confirmed.

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"We have a nominee who has told the United States Senate she is unwilling to impose any limits whatsoever on the authority of the president of the United States for the next 20 months, Cruz said adding that those months will be marked by more “lawlessness” and overreach by the executive branch.

Cruz was the only senator to miss the confirmation vote because he needed to catch a flight for a previously scheduled commitment in Texas, his campaign told NBC News.

"He had to catch a flight for a commitment in Texas," Cruz campaign spokeswoman Catherine Frazier told Kelly O'Donnell. According to a fundraising invitation obtained by Real Clear Politics, Cruz has a fundraiser in Dallas.

In many ways, the opposition to Lynch reflects the contentious and partisan showdowns over the president's nominees during his terms in office. It also speaks to the bitter relationship between Holder and congressional Republicans who say he acted as Obama's "wing man" in matters of policy.

Other Republicans expressed confidence in Lynch’s ability to distinguish herself from her predecessor.

"While I continue to have concerns with President Obama's unilateral immigration actions, I have received written assurance from Ms. Lynch that she will respect both the current court injunction barring implementation of the president's November 2014 executive action as well as whatever final decision results from the federal judicial system's review process, " Senator Kelly Ayotte, R-N.H., said in a statement on Thursday.

It's been a long road.

Senate Majority Leader Mitch McConnell had previously said he would not move forward with Lynch's confirmation vote until disagreements over abortion funding in a human trafficking bill were resolved. Negotiators in both parties reached an agreement and the Senate passed the measure on Wednesday.

She will inherit an agency that has waded recently into high profile civil rights investigations of police brutality in African American communities across the country.

Lynch, 55, is no stranger to civil rights issues.

She grew up accompanying her father, a fourth-generation Baptist minister to meetings to plan boycotts of segregated businesses in North Carolina. When she was a prosecutor in the U.S. Attorney's office, she helped get a conviction of the New York police officer who sexually assaulted Abner Louima, a Haitian immigrant, with a broom handle. It was one of the most high profile police brutality cases of the 1990s and, for Lynch, a career achievement.

She will also head an agency charged with helping thwart terrorist threats.

She has plenty of experience on these fronts.

Lynch was first appointed to the U.S. Attorney post by former President Bill Clinton in 1999. She left for private practice in 2001 and then was appointed a second time by Obama in 2010. During her tenure, her office and helped convict the masterminds of the thwarted al Qaeda plot to attack the New York subway system, and tackled cybercrime and high-stakes financial fraud.

Her office's work has also included dramatic Mafia busts such as prosecuting Vincent Asaro and his crew last year for a $6 million cash and jewel heist from a Lufthansa vault at John. F. Kennedy International Airport in 1978. The movie "Goodfellas" was based, in part, on that heist.

Civil Rights groups applauded Lynch's confirmation and see in her a continuation of Holder's approach to justice issues.

"Lynch’s confirmation has also secured the continued legacy of fair and responsible leadership at the Justice Department by Eric Holder," Wade Henderson, president and of The Leadership Conference on Civil and Human Rights, a broad coalition of civil rights groups, said in a statement on Thursday. "Her indisputable qualifications, character, integrity, and tenacity in the face of obstruction assure us she will serve the nation with distinction."

— with Frank Thorp V