Why does Obama still refer to himself as "President" in his personal twitter?
In America, any politician or military figure is always referred to by the highest title they ever held, even after retirement. You still address
as "President Bush" for example, Rudy Giuliani will always be "Mayor Giuliani".
If you're Colin Powell, you were "General Powell" until you became Sec of State, and now he's addressed as "Secretary Powell."
Barbara Bush is "First Lady Barbara Bush." Hillary was "Senator Clinton" when running in 2008 but if you notice during debates and shit in 2016 they called her "Secretary Clinton" because that was her last highest title.
And it always will be.