One of the most under-reported economic stories of 2019 was the problems with the Repo Market and ‘Not QE’. This article does as good as job of any as explaining whats going on. This is a complicated topic, which is why it hasn’t been covered outside of the financial press, but it seems to me this will have huge implications in the coming years.
Starting in October, largely due to all the government securities being issues, the Fed stepped in and became a net buyer of Treasury securities. Wall Street & the banks treat treasury securities like liquid assets – the problem now being there are so many treasury securities in the market, the appetite is dwindling. Banks are stuffed with treasury securities, foreign interest is stalled. It seems everyone who wants to own a treasury bill has one.

Prior to this, starting in late 2017, the Fed had been (slowly) trying to drain off all the debt it added over the last 10 years. One could argue this was a major factor in the stock market ending down in 2018, with its low in December when the Fed raised rates, and signaled more to come in 2019. In January, the Fed reversed course and signaled lower rates, juicing the stock market to new highs. Now that the Federal Reserve is keeping rates low, they added fuel to the fire by injecting (printing) more money into the system, which has the effect of ending up in the stock market directly. It would seem this is what might be fueling the recent highs in the market.
Another longer term ticking time bomb is all the retirement assets accumulated by baby boomers. As boomers quit accumulating wealth (or die), and they become net sellers of financial assets, that money will be passed back into the economy, flooding the economy with all these T-bills that have been hoarded in these retirement funds. I think this may finally lead to the inflation that has been long predicted by economists when government runs large deficits. Once that money leaves the hands of old savers, and into younger spenders, a lot more money will be chasing the same goods which is a recipe for inflation.
Historical economic theory would assume that rising federal debt would lead to higher interest rates, as supply of debt exceeds demand. So far that hasn’t happened. I think this has been distorted by the huge Baby Boomer appetite for savings, and recent Fed policy is distorting markets by ‘hiding’ this debt on the balance sheet. And because it appears to the public and politicians that ‘deficits don’t matter’, there is no appetite to reign in all the federal debt. So far, its working. But I believe deficits do matter. How long the government can continue to print paper to cover these debts is anybody’s guess. At some point one can assume markets will care? And what will happen when markets do care? That is a question that will be have to be answered sooner or later.