U.N. Ambassador Susan Rice told NBC News on Thursday that she has dropped out of the running to become the next U.S. Secretary of State.

In a letter she reportedly sent to President Barack Obama, Rice said she was saddened by the state of Washington's partisan politics, which she believes would cause her confirmation to be "lengthy, disruptive and costly" to the nation's foreign policy aparatus.

"That trade-off is simply not worth it to our country," she wrote, according to NBC News. "Therefore, I respectfully request that you no longer consider my candidacy at this time."

NBC's Brian Williams is expected to have a full interview with Rice on his broadcast tonight at 10 p.m. EST.

The longtime public servant has been at the epicenter of criticism by congressional Republicans who sought in the final weeks of the presidential election to paint Obama as a weak leader after the tragic attack on the U.S. consulate in Benghazi, Libya on September 11, 2012.

In the wake of the attack, Rice faced the most severe criticism by Republicans like Sen. John McCain (R-AZ), who claimed she was somehow covering up the administration's true agenda by altering talking points to shift the blame from terrorism to an anti-Muslim film that stirred up protests across the region.

Despite their concerns, President Obama called the attack an act of terror from his first remarks about it, and has consistently pledged that a full investigation is underway to determine how it happened. Gen. Carter F. Ham also said recently that U.S. forces have identified several of the main actors behind the attacks.

Read Rice's full letter below.


Amb. Susan Rice Letter to President Obama