I'm not sure this has happened before, and most people are unaware, so I thought a quick note was in order.
If you were previously following the President of the United States on Twitter, when it was Barack Obama, you followed @POTUS.
Twitter has created an account called @POTUS44, which is for President Obama. You are now automatically following that handle.
Twitter redesignated @POTUS to apply to President Trump, and left all of the President Obama followers on that account as well. So, you are now following President Trump at @POTUS.
The same applies, in parallel, to the First Lady and the Vice President.
Meanwhile, these folks have their own civilian twitter handles. President Obama is simply using his old handle (and, by the way, he follows me, just sayin').
So, you may or may not want to update your Twitter accounts accordingly.