Has The Fed Hit A Wall?

I think I am beginning to understand the significance of the current spike in reverse repos. The Fed is no unable to continue bidding up bond prices via quantitative easing without pushing nominal yields into negative territory. Either the Fed relents in their resistance to negative nominal interest rates soon, or the asset bubble will pop.

https://www.zerohedge.com/markets/feds-reverse-repo-hits-all-time-high-485bn-reserves-flood-system