Biden somehow even failed on his best issue.

A few years ago—maybe even a few months ago—President Joe Biden could have waxed eloquent on foreign policy at a moment's notice, highlighting the main talking points on a wide range of issues, unraveling their complexities, and persuasively presenting himself as a man who has immersed himself in the subject for decades. The fact that he failed to do so in Thursday's debate—that he could not shoot down Donald Trump's most easily lobbed libels and lies, much less make a coherent case for his approach to the world's challenges—ranks high among the night's shockers. Some Democrats tried to spin it…