Spin? Like a top or a dreidel?
How can China simply dump the securities?
Russia sold treasuries on the open market just like they buy and sell any other financial instrument. The Feds are required to purchase a treasury note or bond only at the expiration date, not the holder. If an investor "dumps" more bonds than the market can absorb then they have to sell at a discount to entice a buyer to purchase them. That only works when it comes to taking a loss for a greater financial purpose - such as collapsing an existing currency, and one way to jump-start that is with dumping our debt that our government will have to print more trillions to buy back to keep the dollar afloat.
The Dollar's days as a reserve currency are numbered.
I would not be surprised that what Russia is doing by dumping nearly all US Debt treasuries they hold, are test runs to see the way the markets and the Fed react, possibly to determine the best way for China to drop what they claim to have.
Trade wars have consequences.