Chief Justice John Roberts, wary of the potential repercussions should he have cast the deciding vote to nullify the entire Affordable Care Act, backed away from his initial desire to overturn the law for fear that doing so would strip the Supreme Court of its nonpartisan authority.

That revelation is one of a few new insights into the Supreme Court's deliberations on the ACA revealed in excerpts, previewed Saturday by Politico, from a forthcoming book by New Yorker writer and CNN legal analyst Jeffrey Toobin. According to Toobin, Roberts initially wanted to declare the law unconstitutional, but his position grew "wobbly" as he worried that making such a seemingly political move at a crucial point in the presidential race could have undermined the court's future credibility.

From the book:

A complete nullification of the health care law on the eve of a presidential election would put the Court at the center of the campaign … Democrats, and perhaps Obama himself, would crusade against the Court, eroding its moral if not its legal authority. … Gradually, then with more urgency, Roberts began looking for a way out.

What's more, Toobin reports that Roberts' switch was in part prompted by the Court's conservative members' insistence that he join them in striking down the entire law.

“The four conservatives had overplayed their hand with the chief justice," Toobin writes. "By demanding that Roberts kill off the entire health care law, they prompted him to look for some kind of middle ground."

Roberts' reversal on the case was widely publicized immediately after the ruling when, in a rare move, outraged law clerks and other staffers leaked details of the court's deliberations. CBS News' Jan Crawford, in a detailed report following the ruling, revealed that Roberts had switched his vote despite pleas from the court's conservative wing that he remain on their side. According to that report, it was Justice Anthony Kennedy—who is often viewed as a moderate on the court—who most fervently implored Roberts to stick with his original opinion.

Toobin's book, "The Oath: The Obama White House and the Supreme Court," will be released on Tuesday.