Roberts was confirmed on a 78-22 vote in 2005. That's the most votes any justice has received for more than two decades. But some buyer's remorse about Roberts has set in since then.
His liberal critics think he hasn't lived up to his promise to the Senate to "call balls and strikes" as a justice. They think that, with rare exceptions, he has instead been batting for the Republicans: voting to narrow affirmative action programs, weaken the Voting Rights Act, subject abortion to restrictions, deregulate campaign finance and so on.
The conservatives seize on a very big exception: Obamacare. In a 2012 case, all the court's Democratic appointees voted to uphold the Affordable Care Act's requirement that nearly everyone buy health insurance. All the court's Republican appointees except for Roberts voted to strike down that requirement and with it the whole law. Roberts, as the fifth vote, split the difference.
The requirement, he ruled, was unconstitutional. But it could plausibly be reinterpreted as a tax on a person going without health insurance, and if it were so interpreted it was constitutional. If the court can plausibly interpret a law to make it constitutional, he explained further, it should. So Obamacare stayed.
The conventional wisdom on the right became that Roberts had lost his nerve, coming up with a clever rationalization to spare himself criticism from President Barack Obama and his allies. During the 2016 presidential campaign, both Sen. Ted Cruz, R-Texas, and Donald Trump described Roberts as the kind of justice to avoid nominating.
Enter Kavanaugh. He resembles Roberts in some respects. He is comfortably ensconced within the Republican establishment, specifically its Washington, D.C., division. The resemblance in affect was noted before, when Kavanaugh was up for confirmation to his current job. The Washington Post reported in 2006 that Kavanaugh "is widely described as brilliant, affable and disarming, attributes that prevented Democrats from successfully demonizing Roberts."
After watching Roberts in action, though, Kavanaugh's Republican-approved smoothness reads to the left like a stealthy way for a right-wing ideologue to get his way. And to portions of the right it seems like a sign that he won't be a reliable ally when the chips are down.
While Trump was selecting a nominee to replace the retiring Anthony Kennedy and conservatives debated the possibilities, they scoured Kavanaugh's records looking for evidence of this weakness. They found some rulings that concerned them - but they read them as critically as they did because they came to them with the fear of "another John Roberts."
None of this is to say that Kavanaugh is going to have serious trouble getting confirmed. The concern about Kavanaugh on the right will not keep Republicans from closing ranks behind him now that he has been nominated. (It might make for subdued enthusiasm.) Senate Democratic leader Chuck Schumer, D-N.Y., says he will "oppose Judge Kavanaugh's nomination with everything he have," but he will find that he doesn't have much as long as Republicans stay united.
Thus Kavanaugh seems likely to get on the Supreme Court - where, in a final irony, he could well be an obstacle to one of the chief justice's major projects. When offered a choice between a narrow ruling with a broad majority and a broad ruling with a narrow majority, Roberts has tried to go for consensus and even unanimity. That hasn't been Kavanaugh's style as an appeals-court judge. He has written separate opinions more often than most judges, and sometimes has been chided by colleagues for reaching out to decide issues he didn't have to decide.
Although Kavanaugh has a lot in common with Roberts, in other words, he will have the chance to differentiate himself soon enough.