... because he isn't sufficiently Marxist enough.

Left Blasts "Tone Deaf," "Inexcusable" Joe Kennedy Pick - Privileged White Man Who's Not Progressive Enough
http://www.breitbart.com/big-government/2018/01/30/left-blasts-tone-deaf-inexcusable-joe-kennedy-pick-privileged-white-man-who-is-not-progressive-enough/
Some left-wing activists are not thrilled that Democrats selected Rep. Joe Kennedy (D-MA) - a privileged "white man" - to give the response to President Donald Trump's State of the Union speech on Tuesday evening, arguing that it will be tougher for Democrats to attack Trump as a white guy who inherited his wealth with another white liberal who inherited his fortune. They are also slamming Democrats for selecting someone who is not progressive enough. ...

The essential American soul is hard, isolate, stoic, and a killer. It has never yet melted. ~ D.H. Lawrence