Understand that I'm a total novice with regard to economics. Also, while I ultimately have an axe to grind (doesn't everyone?) I'm not trying to do that honing here, I'm simply looking for a sanity check on my "logic" (such as it is). I don't propose to discuss political implications here.
President Trump is proposing a "tax reform" package that is roughly estimated (based on two separate sources I found) at about $5T over 10 years. Let's assume that the cost of this package is not significantly offset by spending cuts (at least not cuts that would exceed proposed spending increases in other programs). So it's reasonable to assume that basically the entire amount would be borrowed, through Treasury securities and similar instruments.
Here it gets a little shaky. Several sources tell me that foreign sources own about 1/3rd of the US government debt. While it's obviously difficult to predict how much of the new debt would be purchased by whom, it's a reasonable spitball estimate to assume that about a third would be sold overseas, assuming interest rates remain at least as high as they are currently, and barring any significant change in overseas perceptions of the soundness of US securities, or of the US economy in general.
This means that foreign sources must come up with about $1.7T in US currency over ten years, thus removing the ability of that much US currency to purchase goods and services from the US (or benefiting from that much US currency being paid out of the US to buy foreign goods and services).
(The objection will be made that money is, uh, fungible, and so currencies other than US currency can be used to purchase US goods. But if I spend my US dollars on T-bills then I will have to convert my rubles to dollars if I want to spend more dollars on US goods and services, and that conversion drives up the "cost" of the dollar, making US goods and services less "attractive". When it balances out the net-net is to have removed that much US money from the pool of cash available to fund US exports.)
The cost to "create" a job in the US seems to be variously estimated at between \$40K and \$100K a year. (I couldn't find any sources that were clear and explicit enough to be worth referencing, alas.) (Most such estimates appear to be orientated towards tech sector jobs, and presumably manufacturing jobs would be "cheaper".) But let's say that a job "costs" $50K/year -- we are "spitballing", after all.
So, dividing the \$1.7B by \$50K times ten years, I come up with 3.4 million jobs lost for a period of ten years, due to the proposed tax cuts.
Where is my "logic" here weakest? Is my spitball aim terribly off anywhere? Are there fatal flaws, or is it simply too fuzzy and "out there" to assess without losing your lunch?
Note: I'm trying to understand the above (presumed) effect in a vacuum of sorts, without considering any of the counterbalancing benefits of deficit spending and related issues. Basically, I'm only looking for criticisms of my "math", and a "but you forgot about ..." answer is only relevant if it somehow modifies or negates that "math". Yes, deficit spending has supposed benefits, but I'm not asking about that.