Chief Justice John Roberts voted against Obamacare, but then — in a move that angered his conservative colleagues — switched his vote as he became convinced that a 5-4 ruling against the law would damage the reputation of the Supreme Court.

Roberts and Justice Anthony Kennedy went through weeks of debate with each other, as Kennedy tried to convince Roberts to strike down the law and Roberts wrangled with Kennedy to create a 6-3 majority in support of the bill, “two sources with specific knowledge of the deliberations,” told CBS News.

That sequence of events tracks with the external debate about the bill after the court heard oral arguments in March. As observers concluded that the court would overturn the individual mandate, Democrats went on offense.

“I’d just remind conservative commentators that for years what we’ve heard is, the biggest problem on the bench was judicial activism or a lack of judicial restraint — that an unelected group of people would somehow overturn a duly constituted and passed law,” President Obama said after oral arguments in an attempt to at least frame an unfavorable decision as politically motivated, in the event that the law was struck down.

As congressional Democrats and liberal pundits repeated the idea that only partisanship could cause the court to overturn the law, Roberts apparently took notice.

“Roberts pays attention to media coverage,” CBS says. “It was around this time that it also became clear to the conservative justices that Roberts was, as one put it, ‘wobbly,’ the sources said.” Other sources denied that the media influenced Roberts’ decision-making process,  and CBS noted that “it is not known why Roberts changed his view on the mandate and decided to uphold the law.”

The report suggests that Robert seized on the tax argument as a way to uphold the law as part of an effort to attract Kennedy by adopting Kennedy’s critique of the Commerce Clause argument.

Roberts and Kennedy each failed to convince the other, of course, and Roberts’ decision certainly frustrated his colleagues.

“The fact that the joint dissent doesn’t mention Roberts’ majority was not a sign of sloppiness, the sources said, but instead was a signal the conservatives no longer wished to engage in debate with him,” CBS reports.