Some of the conservatives, such as Justice Clarence Thomas, deliberately avoid news articles on the court when issues are pending (and avoid some publications altogether, such as The New York Times). They've explained that they don't want to be influenced by outside opinion or feel pressure from outlets that are perceived as liberal.
But Roberts pays attention to media coverage. As chief justice, he is keenly aware of his leadership role on the court, and he also is sensitive to how the court is perceived by the public.
There were countless news articles in May warning of damage to the court - and to Roberts' reputation - if the court were to strike down the mandate. Leading politicians, including the president himself, had expressed confidence the mandate would be upheld.
Some even suggested that if Roberts struck down the mandate, it would prove he had been deceitful during his confirmation hearings, when he explained a philosophy of judicial restraint.
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.
It is not known why Roberts changed his view on the mandate and decided to uphold the law. At least one conservative justice tried to get him to explain it, but was unsatisfied with the response, according to a source with knowledge of the conversation.
Some informed observers outside the court flatly reject the idea that Roberts buckled to liberal pressure, or was stared down by the president. They instead believe that Roberts realized the historical consequences of a ruling striking down the landmark health care law. There was no doctrinal background for the Court to fall back on - nothing in prior Supreme Court cases - to say the individual mandate crossed a constitutional line.
The case raised entirely new issues of power. Never before had Congress tried to force Americans to buy a private product; as a result, never before had the court ruled Congress lacked that power. It was completely uncharted waters.
To strike down the mandate as exceeding the Commerce Clause, the court would have to craft a new theory, which could have opened it up to criticism that it reached out to declare the president' health care law unconstitutional.
Roberts was willing to draw that line, but in a way that decided future cases, and not the massive health care case.
Moreover, there are passages in Roberts' opinion that are consistent with his views that unelected judges have assumed too much power over American life, and that courts generally should take a back seat to elected officials, who are closer to the people and can be voted out of office if the people don't like what they're doing.
As Roberts explained in his opinion:
"The framers created a federal government of limited powers, and assigned to this Court the duty of enforcing those limits. The Court does so today. But the Court does not express any opinion on the wisdom of the Affordable Care Act. Under the Constitution, that judgment is reserved to the people."
Regardless of his thinking, it was clear to the conservatives that Roberts wanted the court out of the red-hot dispute.