By Michael McGough

Sen. Ted Cruz, who urged the Senate to “swiftly” confirm John G. Roberts as a Supreme Court justice in 2005, threw Roberts under the campaign bus in Wednesday’s Republican presidential debate.

“It was a mistake when he was appointed to the Supreme Court,” Cruz said. “He’s a good enough lawyer that he knows in these Obamacare cases [that] he changed the statute, he changed the law in order to force that failed law on millions of Americans for a political outcome.” (The Wall Street Journal op-ed page today printed Cruz’s 2005 and 2015 statements side to side.)

Roberts should be used to being double-crossed by presidential hopefuls. When he was nominated to be chief justice he had every reason to believe his fellow Harvard Law School graduate Sen. Barack Obama of Illinois would vote yes. But then, as the Washington Post reported, Obama’s presidential ambitions intruded:

“It was the fall of 2005, and the celebrated young senator — still new to Capitol Hill but aware of his prospects for higher office — was thinking about voting to confirm John G. Roberts Jr. as chief justice. Talking with his aides, the Illinois Democrat expressed admiration for Roberts’s intellect. Besides, Obama said, if he were president he wouldn’t want his judicial nominees opposed simply on ideological grounds.

“And then [Pete] Rouse, his chief of staff, spoke up. This was no Harvard moot-court exercise, he said. If Obama voted for Roberts, Rouse told him, people would remind him of that every time the Supreme Court issued another conservative ruling, something that could cripple a future presidential run. Obama took it in. And when the roll was called, he voted no.”

Presumably Obama feels a bit of remorse, given that Roberts voted not once but twice to uphold challenged provisions of Obama’s key legislative accomplishment, the Affordable Care Act.

It isn’t just politicians who lose their sense of proportion when the topic is John Roberts. Activists on the right share Cruz’s outrage that the chief justice “propped up” Obamacare; activists on the left will never forgive Roberts for voting to invalidate a key provision of the Voting Rights Act and to join Justice Anthony Kennedy’s majority opinion in Citizens United, a decision that some progressives view as morally equivalent to Dred Scott.

For conservatives, Roberts’ great sin is a supposed oversensitivity to public opinion and media coverage; for liberals, it is a canny and covert agenda of dismantling liberal precedents in the service of the conservative philosophy that attracted a young John Roberts to Ronald Reagan.

According to a fascinating review of Roberts’ record as chief justice by Brianne Gorod of the liberal Constitutional Accountability Center, the story “is not altogether a simple one.”

“To be sure,” Gorod writes, “John Roberts is a very conservative justice, one who votes to move the law sharply to the right far more often than not…. But there are other areas as well — areas in which Roberts’ deep concern about the institutional legitimacy of the court and his reputation as its chief justice can lead him to put law over ideology. Those areas may be few, but they can also be important.”

Important enough to have an ambitious former supporter like Ted Cruz turn on you.