I think the "unwinding" was Fed stopping QE, which is slightly different - they were buying bonds on the market (not as emergency liquidity) to prop up asset prices (buy bonds -> reduce interest rate -> investors seek other sources of returns -> buy stocks -> stock prices go up... same with real estate). Bonds mature (literally disappear), so if you want to keep propping up asset prices, you must keep buying new bonds as the ones you own mature. The Fed was doing that for a while, then tried to slowly stop, ween the market off the cheap money (because if the patient is supposed to be healthy, s/he should be able to survive and thrive without drugs). Trump threw a tantrum (I guess he knew/suspected that Fed was the only/main thing propping up asset prices, without Fed the market would crash/stop increasing, which isn't good for elections because politicians always get the blame), the markets weren't happy either (basically NIMBY - you're invested so you want to keep the value of your assets as high as possible).