Tonight on AC360: Gonzales: Roberts still conservative

In a major victory for President Obama, the U.S. Supreme Court upheld the controversial health care law known as Obamacare. The justices voted 5-4 that, among other measures, the individual mandate requiring people to have health insurance is valid as a tax, which is within Congress's power.

Chief Justice John Roberts, who was nominated by President George W. Bush, sided with his liberal colleagues.

CNN Legal Analyst Jeffrey Toobin had anticipated a different ruling. "I was wrong. I thought that argument went very badly. I was very critical of Donald Verrilli," said Toobin. Solicitor General Verrilli made his argument before the Supreme Court in March. Back then, Toobin called his presentation “a train wreck."

"I thought that the argument on the commerce clause was really the core of this case, and all of the conservative justices, including Chief Justice Roberts, and especially Justice Kennedy, were very skeptical about whether the commerce clause was a justification for this law. They voted against the commerce clause, but this taxing power issue really snuck up on us and it certainly snuck up on me," explained Toobin.

Former Attorney General Alberto Gonzales, who served during the Bush administration, told CNN's John King that Roberts' "legacy has yet to be written." He said he still believes Roberts is a conservative justice and "will decide most cases in that fashion."

Watch a preview of the interview and tune in at 8 and 10 p.m. ET to see the entire conversation.