It might be that the Trump administration is that sloppy. Or it might be that they trust that they have so undermined the credibility of the press by continually calling it fake news that they will be able to ignore or brush off any reporting that points this out. They are operating in a fact free zone.
If that's not enough, there is more. Where does this extra $2 trillion over 10 years come from? It's existence comes from an assumption that the economy will grow by 3% a year for a decade. How likely is that?
Well, since 1948, the longest stretch during which GDP growth exceeded 3% was 6 years. (From 1961 to 1966, when Johnson's New Deal was increasing government spending, defense spending for Vietnam was just ramping up, and the baby boomers were starting school and driving their parents to buy more housing, clothes, and cars.) It has been eleven years since GDP growth has been as high as 3% (exactly 3% in 2005, and 3.1% the year before that.) In this century - since 2000 - GDP growth has not even averaged 2%, much less 3%.
So is there reason to believe that economic growth will bump up 50%? (3% is 50% more than 2%.)
Curiously, per capita GDP growth has been incredibly stable since after the Civil War. Here it is by decade. (Source data here.)
Note that in only one decade has per capita GDP growth been more than 3%; in the 1940s, when the US was spending a huge amount of money first fighting Nazis and then rebuilding Europe and Japan, per person GDP growth was nearly 4%. World War 2 was the catalyst. Pull out that decade and you can see that per capita GDP growth has never averaged 3% for a decade.
And here is a phenomenal statistic. Pull out the 1940s and the average per capita GDP growth since the 1870s has been 1.88%. The average GDP growth in this century? 1.88%.
GDP growth bounces over 3% in healthy and normal decades but it does not stay much above 2% for any length of time without a growth in the workforce. A growth in the workforce depends on immigration and birth rate.
So, will GDP bounce up to 3% for a decade? Only if Donald decides to encourage immigration. (Insert laughter here.) Millennials will cause a growth in the workforce during this next decade to offset baby boomer retirements but it won't be enough to cause a noticeable surge.
Trump's budget plan doesn't just use the same $2 trillion to simultaneously pay down debt and cut taxes. It forecasts this additional $2 trillion by assuming GDP growth we've only experienced in one out of the last fourteen decades. It's not just that he and Mulvaney are spending this money twice; it's imaginary money.
83% of what Trump says ranges from half-true to pants on fire. Only 17% of what he says is mostly true or simply true. It's little wonder that with such disregard for facts he would put out a plan that shows such utter disregard for simple arithmetic or reasonable assumptions. He continues to show his contempt for Americans' ability to reason. So far, assuming that we're all stupid has worked out well for him. It doesn't seem like it'll work out as well for the rest of us.