Officials in Portland, Oregon, said on Sunday they were braced for an escalation of protest-related violence that has convulsed the city for three months, citing social media posts vowing revenge for a fatal shooting amid weekend street clashes between supporters of President Donald Trump and counter-demonstrators Subscribe: http://smarturl.it/reuterssubscribe Reuters brings you the latest business, finance and breaking news video from around the globe. Our reputation for accuracy and impartiality is unparalleled. Get the latest news on: http://reuters.com/ Follow Reuters on Facebook: https://www.facebook.com/Reuters Follow Reuters on Twitter: https://twitter.com/Reuters Follow Reuters on Instagram: https://www.instagram.com/reuters/?hl=en