Paid for by tariffs. Trump is going to get other countries to pay for the funding of new infrastructure, manufacturing and research within the US. He will sell the fruits of that labour at home, for cheap, while keeping enough in reserves to cover for the financial correction.
There will be a financial correction during Trumps' term, with a drop in the markets of anywhere between 20%-40%. This has to happen and the first country to go through it - which usually is America, will be the one to ride the wave to a healthy market.
Trump seems to be making the right moves to slash overheads and bring in surplus cash before the crash of the markets. I also don't think he will live to see Christmas. He is acting not like a man who isn't afraid to die, and instead acting like a man who knows he is going to die and is off out with a vengeful bang.