How strong is the federal case against Donald Trump?

In the ballroom, in the bedroom and even in the bathroom - that's where Donald Trump allegedly kept classified documents. Now he's being charged on 37 criminal counts for his mishandling of confidential papers he took with him when he left the White House. Among other things, Trump is accused of willful retention of national defense information including nuclear and weapons programs and conspiracy to obstruct justice.
The FBI seized a cache of sensitive government documents during a search of Trump's Florida residence in August. Trump is the front runner for the for Republican nomination for next year's presidential election. The charges against him will not prevent him from campaigning or from taking office if he wins. Trump says the charges against him are politically motivated.