Chief Justice John G. Roberts Jr. attends the State of the Union speech at the Capitol in January 2014. (Larry Downing/Reuters)

Chief Justice John G. Roberts Jr. became an unlikely target of conservative fire at the Republican presidential candidate debates Wednesday night, with several candidates questioning his Supreme Court nomination by President George W. Bush a decade ago.

Sen. Ted Cruz of Texas and Louisiana Gov. Bobby Jindal said the selection of Roberts was a mistake, and even former Florida governor Jeb Bush seemed to second-guess his brother’s choice.

“John Roberts has made some really good decisions, for sure, but he did not have a proven, extensive record that would have made the clarity the important thing, and that’s what we need to do,” candidate Bush said. “And, I’m willing to fight for those nominees to make sure that they get passed. You can’t do it the politically expedient way anymore.”

Roberts did not escape criticism even during commercial breaks of the CNN-sponsored debate.

The conservative legal group Judicial Crisis Network aired a commercial telling voters to “demand justices with a proven record of upholding the Constitution. We can’t afford more surprises.” It ends with a photo of Roberts, along with Justice Anthony M. Kennedy and former justice David Souter, two other Republican Supreme Court nominees whom conservatives have said that they regret.

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Roberts was supported unanimously by Republican senators in his confirmation and was hailed as the prototype of a successful Supreme Court nominee for his description of the role of a judge and the value of judicial restraint.

“Judges are like umpires,” Roberts said at the time. “Umpires don’t make the rules. They apply them. The role of an umpire and a judge is critical. They make sure everybody plays by the rules. But it is a limited role. Nobody ever went to a ballgame to see the umpire.”

But the right’s unhappiness with Roberts comes from two calls, both involving the Affordable Care Act.

In 2012, Roberts cast the deciding vote upholding the act, saying that the court was bound to find a way to save Congress’s acts from constitutional challenge if there was a legitimate way to do it. In June, he was in a larger majority that rejected a reading of the law that would have drastically cut back the number of Americans it covered.

Most Supreme Court observers find those votes anomalies rather than evidence of a drift to the left. Indeed, studies have shown that the court that Roberts heads is among the most conservative in history.

But the most recent term featured headline-grabbing victories for liberals saving Obamacare and declaring a constitutional right for same-sex couples to marry. Even though Roberts was a dissenter on marriage — “Just who do we think we are?” he wrote in a lengthy rebuttal of the majority decision — conservatives take a dim view of the current court.

A Gallup poll conducted in July showed Republican approval of the court’s work at 18 percent, a record low. And less than a quarter of Republicans said that they had a favorable opinion of Roberts, compared with 43 percent who viewed him unfavorably.

Those numbers could explain the newfound criticism from those seeking the Republican presidential nomination.

After some needling by Jeb Bush, Cruz acknowledged that he had been an enthusiastic supporter of Roberts at the time of his nomination.

“I’ve known John Roberts for 20 years. He’s an amazingly talented lawyer, but, yes, it was a mistake when he was appointed to the Supreme Court,” Cruz said. Not only were Cruz and Roberts both clerks to the late chief justice William H. Rehnquist, but Cruz recruited Roberts to help with the Florida presidential recount in 2000, when Cruz was coordinating conservative legal talent.

But Cruz said that former president Bush passed over a more conservative choice because he felt Roberts would be more confirmable.

“You know, we’re frustrated as conservatives,” he said. “We keep winning elections, and then we don’t get the outcome we want.”

Liberals, on the other hand, have sharply criticized the Roberts court for a string of conservative victories. Roberts has been in the majority in rulings that sided with businesses over consumers, curtailed affirmative action, limited the reach of the Voting Rights Act, struck down school desegregation plans and removed restrictions on corporate and union campaign spending in Citizens United v. FEC.

During the earlier debate among candidates lower in the polls, Sen. Lindsey O. Graham (S.C.) defended Roberts.

“He’s one of the most qualified men to ever come before the United States Senate, and I don’t agree with his decision [on the Affordable Care Act], but 99 times out of 100, I will,” he said.

Former senator Rick Santorum (Pa.) agreed. “Justice Roberts had a long record, and it was a long, good record,” he said. “And so he made a bad decision on — a couple of bad decisions on Obamacare — but he’s made a lot of great decisions, too.”