If someone took over Trump's twitter and detailed how bombers were in-route to take out North Korea's nuclear capability, would Kim Jong Un wait for independent confirmation before he launched his missile(s)?
So that's the worst case; the reality will be somewhere between that and doing nothing.
Within the bounds of the Constitution, Washington can regulate however its people's representatives see fit. Over the past 20 years, most people have sided with companies like Google and Facebook because they produce products that are amazing and addicting. This tide is changing; their products are becoming less and less novel, and its becoming increasingly apparent that horribly few of these companies act with any sense of ethical responsibility or discretion.
Do you really think it's in the nations best interest that _Twitter_ is being treated as an official source of news from the POTUS?
Whether Twitter is the best medium for that is another question, given the character limits and demonstrated unprofessional behavior by the platform owner. I bet his account gets a lot more exposure there than a page on whitehouse.gov would.
I think Google's managing director in Brazil was arrested a couple times for refusing to give some information to Brazilian law enforcement or refusing to remove some content.
Imagine this, they are one button away from taking away the US president main mean of communication.
This is akin to a country doing a military parade, showing off their arms.