Twitter's stock price was down as much as 12.3% on Monday after outgoing US President Donald Trump was permanently banned from the platform. After closing at $51.48 per share on Friday, the US-based social networking service saw its stock price open down at $47.16 a share on Monday, then fell to as low as $45.15 per share shortly after opening bell at 9.30 a.m. on the US East Coast (1430GMT) ...