The Post devoted a business section article to Newt Gingrich's supply side economics. It would have been useful to note the findings of the research on this topic, for example this Congressional Budget Office study. It found that even in a best case scenario the additional growth sparked by a tax cut could replace less than a third of the lost tax revenue. Even this effect would be temporary, with slower growth in later years implying larger deficits.
The Post should not just throw Gingrich's assertions out to readers as though they might be true. There is extensive research on this topic which the Post's business reporters should be familiar with - its readers almost certainly are not.