He was looking for someone with the ability to win over Justice Anthony Kennedy, the crucial swing vote.

“[Obama] was very struck, when he met with her, about how thoughtful she was as a judge,” says the source. “He believed she had a precise approach to cases that would be effective in winning over Kennedy when possible.”

The president considered Sotomayor’s opinions to be “rigorous, precise, not overly flamboyant.” Reports have called her more workmanlike than visionary – a precision that impressed Obama, who is looking to turn narrow decisions his way.

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Sotomayor’s colleague and former Yale Law School professor, Judge Guido Calabresi, became aware of the anonymous sniping after she joined him on the 2nd Circuit in 1998. He eventually concluded that the complaints reflected sexism among male attorneys.

“They didn’t like the idea of a woman being as strong as her male colleagues,” Calabresi said in an interview.

He further characterized Sotomayor as a “wonderful colleague” who doesn’t mince words. He said she had “in a not insignificant number of cases changed my mind . . . both by charm, but mainly by the force of her legal argument.”

The forcefulness — or fearlessness — showed even before Sotomayor graduated from law school. While she was at Yale in the late 1970s, The Washington Post reported at the time, she filed a discrimination complaint against a Washington law firm after a partner asked her questions that she considered objectionable.