Tesla Stock Falls 21% in Worst-Ever Trading Day

$Tesla (TSLA.US)$ shares closed down 21% today.

Declines started premarket and worsened as General Motors Co. said it would take a $2-billion equity stake in Nikola Corp. and partner with the fledgling truck maker to engineer and manufacture its Badger pickup.

The news lifted $Nikola (NKLA.US)$ shares by 41% while $General Motors (GM.US)$ Rose 7.9%.