I thought that "progressive" and "regressive" refer to what percentage tax you pay given what bracket (in dollars, not in percentile) you are. I would have thought that the 45% mentioned in the article is proof of how many Americans are poor, not that the tax plan is progressive.
Even with a moderately regressive income tax the rich will be paying more total tax even though they are paying a smaller percentage of their income as tax. Therefore you can not make any conclusions about the fairness of a tax by saying that the top 20% of earners pay 80% of the total amount of income tax (it would have been absolutely crazy if this was not the case, unless everybody had the same income).
As such, I do not see how this article can be used to say anything about whether the tax is progressive or regressive (and as you mentioned, whether it is fair altogether).
Even with a moderately regressive income tax the rich will be paying more total tax even though they are paying a smaller percentage of their income as tax. Therefore you can not make any conclusions about the fairness of a tax by saying that the top 20% of earners pay 80% of the total amount of income tax (it would have been absolutely crazy if this was not the case, unless everybody had the same income).
As such, I do not see how this article can be used to say anything about whether the tax is progressive or regressive (and as you mentioned, whether it is fair altogether).