If he left the highest court in the land, Donald Trump would nominate his replacement. The Senate rules are now such that whoever that is would be confirmed relatively easily.
Kennedy is a classic swing vote on the Supreme Court and thus its most important member. Sometimes he sides with the high court's four more progressive members. Sometimes he sides with the court's extremely conservative members.
Hence, he's the only remaining moderate and defiantly so. He has been the critical vote protecting LGBT rights, women's rights, reproductive rights, and civil rights. He doesn't have a sterling record for progressive causes, but he certainly would be better than any arch conservative Trump would nominate.
Because Supreme Court justices serve for life, a second Trump nominee on the court would give conservatives a clear majority of votes for the next several decades, because the President almost certainly would nominate someone well under fifty years of age.
The editorial was obviously designed to catch Kennedy's eye, given its placement and the fact he almost certainly will see it. Hopefully he won't ignore its cogent argument, a sample of which now follows.
"Do you want to give your seat to a President whose campaign and administration are under criminal investigation, whose closest aides have been indicted or have pleaded guilty to federal crimes? A President with so little regard for or understanding of the role of the judiciary, the separation of powers, and the rule of law? A President who nominated to the federal bench someone who called you a 'judicial prostitute'?"
Hopefully Kennedy will see the piece and, most importantly, reconsider his decision to retire, if he indeed is considering that. He's 81, but he's not the oldest justice currently serving on the court. And the oldest in Supreme Court history was Oliver Wendell Holmes Jr., who stepped down at ninety.
I'm wondering if some smart people will start a movement for every progressive American to mail a copy of the Times editorial to the justice. If that starts up, I'll post details on this blog.