From the crime bill to immigration to health care, Mr. Biden is facing attacks for his role in policies that Democrats can argue in good faith worked. Crime rates went down; Mr. Obama staved off a crisis on the southern border while protecting hundreds of thousands of Dreamers from deportation; and after Obamacare was put in place, the number of Americans without health insurance fell to an all-time low.

The arrogance of the present scoffs at these Democratic achievements. Instead, it declares that crime rates would have fallen even without Democratic toughness, that our nation’s immigration challenges would have been eased without conventional law enforcement, and that our health care system is so broken that Obama’s signature legislative achievement must be completely undone.

It’s one thing to attack Mr. Biden’s vote on the Iraq war. That was a Republican administration’s policy; it faced substantial Democratic opposition; and now even Republicans have largely rejected their own president’s great gamble. It’s another thing entirely to reject Democratic accomplishments of the recent past.