Supreme Court Chief Justice John Roberts went from savior to goat within conservative circles the moment he sided with four liberal justices to uphold President Obama's health care overhaul, giving new life to reforms that would have died without his backing.

Court observers had expected the split decision, but most were betting a perennial swing vote, Justice Anthony Kennedy, not Roberts, would break with conservatives and back a law that Republicans are eager to defeat.

(View the Supreme Court's ruling)

So, when Roberts said the Patient Protection and Affordable Care Act fell within Congress' power to levy taxes, the appointee of President George W. Bush ignited a wave of Republican indignation.

"I am stunned and shocked, somewhat confused, by the decision, by the nature of the decision, by the nature of the majority and by the nature of the reasoning," said Sen. David Vitter, R-La.

Rep. Jack Kingston, R-Ga., took to Twitter after hearing the court's ruling. "I feel like I just lost two great friends: America and Justice Roberts," he wrote.

Roberts, the architect of a 2010 decision allowing unlimited campaign spending by outside groups, was already a demon of sorts in Democratic circles. Indeed, the man whose law Roberts rescued, then-Sen. Barack Obama, voted against Roberts' appointment to the court in 2005. Like many Democrats, Obama feared Roberts was too conservative.

But Roberts is only the latest Supreme Court Justice who zigged when expected to zag.

Chief Justice Earl Warren, a former California governor appointed by Dwight Eisenhower, was expected to be a conservative voice to the bench. Instead, he was instrumental in a series of progressive decisions that prompted Eisenhower to complain that Warren was the "biggest damned-fool mistake I ever made."

Justice Hugo Black, an appointee of President Franklin D. Roosevelt, was a former member of the Ku Klux Klan, who became a leading figure on the court's liberal wing.

Yet, while Roberts' shift was not unprecedented, it was, in the eyes of conservatives, unforgivable.

"No matter what John Roberts does in the future, this is his legacy," said one GOP strategist. "He's dead to our cause."