U.S. Treasury Cash Balance

Following the debt ceiling deadline of March 2017, cash in the U.S. treasury plunged to almost zero to push up bank reserves and that subsequently pushed up the stock market.

This is also seen in the increase in the monetary base.

So while we haven't heard anything on QE4, we actually had an increase in monetary base due to the depletion of cash at the U.S. treasury to prop up the stock market one last time before the debt ceiling holiday expired in March 2017. Now that that cash is fully used, there is nothing that will stop the stock market from declining.