In the immediate aftermath of the announced deal, they sent bitcoin’s price tumbling well below $20,000, its support of the last two weeks. Hours later, prices were bounding above the threshold. But by the afternoon, the largest cryptocurrency by market capitalization had plummeted under $19,000 for the first time since mid September. BTC was recently trading at about $18,500, down more than 10% over the previous 24 hours and its first time under $19,000 since mid October.