Mr. Obama’s dismantling of boundaries isn’t restrained to questions of law; he blew up certain political ethics, too. And yes there are—or used to be—such things. Think what you may about George W. Bush’s policies, but he respected the office of the presidency. He believed he represented all Americans. He didn’t demonize.

Today’s divisive president never misses an opportunity to deride Republicans or the tea party. He is more scornful toward fellow Americans than toward Islamic State. This too sets new norms. Senate Minority Leader Harry Reid now uses the chamber to accuse individual citizens of being “un-American.” Asked recently what “enemy” she was most proud of making, Mrs. Clinton lumped “Republicans” in with “the Iranians.” Ted Cruz rose to prominence by mocking his Republican colleagues as “squishes.” Mr. Trump has disparaged women, the other GOP contenders, Iowans, wives, the disabled, Jews. (Granted, he might have done this even without Mr. Obama’s example.)

Can such leaders be trusted to administer Washington fairly? Of course not. That guardrail is also gone. Mr. Obama egged on his IRS to target conservatives, used his Justice Department to exact retribution on politically unpopular banks, and had his EPA lead an armed raid of an Alaskan mine. Is it any wonder that Bernie Sanders’s climate plan, released this week, includes a vow to bring criminal prosecutions against “climate deniers”? And he would.