Remember when Republicans feared the bungling diplomacy of a vain, inexperienced president and vowed to stop him before he destroyed our security? In 2014, Senate Republican leader Mitch McConnell (Ky.) warned that President Barack Obama was “inflexibly clinging to campaign promises.” If the novice president expected Congress to “stand idly by and do nothing while he cuts a bad deal,” House Speaker John A. Boehner (Ohio) said a year later, he and his party had two words for Obama: “Hell no!”

“Our allies don’t trust us; our enemies don’t fear us; and the world doesn’t know where America stands,” went a 2015 presidential campaign ad for Sen. Marco Rubio (Fla.). And one Republican foreign policy analyst even wrote that negotiations — with Iran, not North Korea — have “become humiliating, not least because our diplomatic body language is telegraphing an eagerness for a deal — any deal — with such clumsy obviousness that only the dumbest opponent could fail to notice it.”

I’m fairly sure I’m quoting that last one correctly, because I wrote it, back in early 2015. And I think I was right: I remain deeply skeptical about the way the Iran deal was negotiated. But compared with the unconscionable mess that President Trump just left behind at his Singapore “summit” with Kim Jong Un, Obama’s long and arduous discussions with Iran look like Klemens von Metternich convening the Congress of Vienna.

When it comes to foreign affairs — when it comes to everything, really — Trump is weighed down by inexperience, bedeviled by vanity and hobbled by impulsiveness. He’s a celebrity playing at president.

He’s everything, in other words, that Republicans feared Obama would be. ...