He can't seem to articulate a good answer to the repeated question, "How are you gonna pay for it?"
1) It would generate significant economic activity by putting money into the hands of people who spend it at the highest rates, thus generating tax revenue
2) It would means test people off welfare programs, saving a significant chunk
3) The top-end can easily afford to pay a higher tax rate since they've enjoyed almost all of the economic gains for decades
4) Maybe it won't be 100% deficit neutral, but I don't recall slack-jawed yokels standing around asking how we gonna pay for $700+ bln per year on military programs that get moth balled without ever seeing combat, or $3 trillion on a useless war in Iraq, or trillions in tax cuts for companies like Amazon who push working Americans to the brink.