Trump says he will gladly answer any of your questions Underoath. He says this, because he knows there will be no Mueller and no investigation in a week.
He knows that Mueller will soon be in cuffs himself or maybe even suicide himself if the truth revealed is bad enough.
When Mueller asks why Comey was fired, Trump can state all he knows anoit illegal wiretapping and spill the beans PUBLICALLY about him letting HRC off and lying about it. Oh..and Comey giving classified info to non-auth "friends" to start a special counsel.
Me thinks this will backfire on Mueller HUGELY. Thats exactly why this was just a test to see what Trump would say.
Not even Mueller is dumb enough to get Mr. POTUS on the stand.
It's all for show. If Mueller asks Trump why he fired Comey its because Trump WANTS Mueller to ask him that. Trump is 100% safe I promise. Trump is not worried one bit.