-- How much "the US needs to finance itself" is not some fixed number. Markets reconcile the demand and supply for dollar-denominated assets. Thus far, Asian central banks, for example, have demanded, and we have supplied. We have, admittedly, supplied in abundance, but that is in part because the price has been low. As the price rises, we will do less.
I actually highly doubt that this is true at all. Over the short and medium term at least, I doubt the borrowing desires of the federal government are affected at all by the price of borrowing. And, over the longer term, more such borrowing increases the need to borrow even further to cover debt servicing obligations. Plenty of countries have piled on ever increasing amounts of debt at very high interest rates.
The government is not a rational actor in any sense. And, as long as we have people in power who see no conflict between huge spending increases and massive tax cuts - and, in fact, advocate piling on trillions in new debt - there's no reason at all to think that an uptick in the cost of borrowing would even register.