Astute observers should be more sanguine. The Fed cannot reduce its QE purchases of fixed-income securities as long as the U.S. economy is growing at a rate slower than the rate of new sovereign debt issuance. It would take an indefinite number of years for GDP growth to obviate the need for new QE buys but that timeline is about to become irrelevant. The BOJ's war on the yen is in full swing and central banks in other developed countries will print money to keep pace.
Using printed fiat currency to fund infrastructure improvements is hilarious. Arguing that such stimulus goes "directly into the economy" is a polite way of ignoring the immediate inflationary effect it will have on commodities. Steel, copper, cement, silicon-based compounds, forestry products (pulp / paper / plywood), and other construction inputs would be the first to skyrocket in price as QE-backed bids clear them from the market. This will not be fun to watch at all.