Mainly the algo effect of sell on the news. As with many technical events/truisms, they are sort of a self fulfilling prophesy. People expect a sell off, so they short, and the result is....a sell off! Then stop losses get triggered and other weak longs get spooked and sell. Once the day traders get involved in a stock it can really distort prices in the short term.
Lately, TSLA has not been shrugging off the short selling and it's had a lasting effect in many cases, probably due to being in the merger twilight zone. I don't think this twilight zone will last through the er, though. I expect a big move from the er, merger or not. To be clear, I think the market reaction tomorrow will be short lived and therefore inconsequential bc er is soon.
My best guess is a drop tomorrow, trade between 195 and 205 until er, then BAM.