It's because the Supreme Court is the least political branch that Justice Ginsburg can say what everyone knows about Trump, including all Republicans. 

They can't say it, that's understable. 

She can, that's good. 

He's an incompetent phoney who isn't up to the most trivial job. He can't even read off a teleprompter. He's a total narcissist. It would be hard to imagine someone less up to the job than Donald Trump

Bless her for speaking the truth. 

He isn't even equal to the most corrupt and mentally ill President we've probably ever had.