The Fed started reducing their balance sheet, unwinding QE1, 2, and 3. They sold some of their assets, and burned the cash. So that took some liquidity out of the system.
Second, as a result of the last big economic crash, banks are now required to hold larger chunks of Tier 1 capital. So that took some liquidity out of the system.
Then Deficit Donald took office and started doubling the deficit to a trillion dollars. When the banks bought all that debt, that took a shit ton more of liquidity out of the system.
So now the Fed is reversing course and enacting QE4.
And Deficit Donald doesn't have the decency to even tweet a thank you. It would take, what...ten seconds?
We enter a Brave New World of macroeconomics. The Fed finances historic deficits and tax cuts for the uberwealthy by placing hundreds of millions of US debt on it's balance sheet. Those hundreds of millions go to all kinds of things from Ford Class aircraft carriers to disability for those not covered under Social Security to Medicaid to Student Loans (ok DeVos is ending that, of all things) tax cuts for employers covering workers HC insurance ….. Most of these "items' increase economic activity either through directly employing people, or spending by people getting money.
However when the Treasury pays the Fed interest either with taxes or new debt, the interest is magically paid back to the Treasury. And when a bond financing debt that the Fed bought matures …. the underlying debt is simply erased from the Fed's balance sheet.
Thus the debt is actually better than free money. It's never really repaid, and it earns interest for the borrower, the US Treasury. And the increase in economic activity really happened in that people did get to spend money! Our parents might make some crack about crack cocaine. Perhaps more accurately it is like Steven Earl Keen. The Road Goes on Forever and the Party Never Ends.
The actual money supply doesn't increase, so it is not inflationary from more dollars chasing the same goods/services. But it is like an addictive drug in that without continued injections of liquidity (or free borrowing) the economic engine ….. stops.