Jennifer Rubin: How Biden gets under Trump’s skin

President Donald Trump insults and attacks Democratic presidential contenders. He doles out derisive nicknames. Rarely, however, does he defensively respond to an attack (real or perceived) against him. He's done it twice in less than a week in response to former Vice President Joe Biden, so it's worth examining how and why Biden manages to annoy Trump.Biden's focus in his announcement video on Trump's infamous remarks after Charlottesville did what few politicians do effectively: call out Trump