Senator John Kerry
Senator John KerryReuters

President Barack Obama has decided to nominate Senator John Kerry to be the next secretary of state and could make a formal announcement as early as next week, a Democrat who spoke to Kerry told CNN on Saturday.

The expected nomination comes after UN ambassador Susan Rice decided on Thursday to withdraw her name from consideration for the post.

Rice asked Obama not to pick her as his next secretary of state, after becoming a lightning rod for Republicans over the raid on the U.S. consulate in Benghazi.

Rice’s role as a top defender of the administration over the attack, which killed the U.S. ambassador to Libya on September 11, drew her into a furious row with Republicans.

Republicans pounced on Rice after she said on September 16 that the Benghazi attack was a "spontaneous" reaction to an anti-Muslim video, using CIA talking points she now admits were wrong.

If confirmed by the Senate, Kerry would replace current Secretary of State Hillary Clinton, who plans to leave her post within the administration.

Kerry, the senior senator from Massachusetts and the Democratic Party's 2004 presidential nominee, is noted for the experience, gravitas and relationship-building skills that could help him succeed as the United States' top diplomat.

Sen. John McCain, R-Arizona, recently jokingly referred to Kerry as "Mr. Secretary."

Kerry lost the 2004 election to incumbent President George W. Bush, who won the Electoral College vote 292 to 252 and racked up three million more votes than Kerry.