According to WSJ, today, 36% of American households today pay no income taxes, and that number would grow to 50%.
That is 31 million households that have been paying some taxes would under the Trump plan not have have any tax liability. They would merely send the IRS a note: "I win."
Also, small business income is currently subject to rates of as much as 39.6%. Under Trump's plan, businesses taxes would be capped at 15%.