Up until now, Roberts has stayed silent on President Trump’s repeated attacks on the judiciary—including on Roberts himself, over the ruling in favor of Obamacare in 2012. On Tuesday, however, Trump criticized federal district judge Jon Tigar for blocking his executive order targeting asylum-seekers on the southern border. “This was an Obama judge,” he told reporters before venting other grievances about the Ninth Circuit Court of Appeals and hinting at some kind of retaliation.

Chief Justice John Roberts explicitly rejected Trump’s description in a statement Wednesday. “We do not have Obama judges or Trump judges, Bush judges or Clinton judges,” he told the Associated Press. “What we have is an extraordinary group of dedicated judges doing their level best to do equal right to those appearing before them. That independent judiciary is something we should all be thankful for.”

While a public rebuke of the president by the chief justice is extremely rare, Trump is also more openly hostile to the federal judiciary than any of his modern predecessors. He argued on the campaign trail that Judge Gonzalo Curiel couldn’t be trusted to oversee the Trump University fraud lawsuits in 2016 because he is “a Mexican.” (Curiel is from Indiana.) Trump also attacked multiple “so-called” judges who ruled against the Muslim ban last year, prompting a rare critique from Justice Neil Gorsuch during his Supreme Court confirmation process.

So, why now? Roberts may have decided to intervene after Trump told reporters that the judge’s ruling was “not law” and suggested he would escalate his campaign against the courts. “I’ll tell you what, it’s not going to happen anymore,” the president said on Tuesday. The chief justice and his colleagues have also spent recent months publicly reaffirming their nonpartisanship after the corrosive battle to confirm Justice Brett Kavanaugh dealt a serious blow to the Supreme Court’s legitimacy and perceived independence.