What might be a problem if the US also pursues a negative interest rate policy?

How might it make sense for a trader to buy a bond with negative interest rate. (hint: how does the investor make a capital gain?)

How did the low interest rate on European bonds affect demand for US bonds? (think of the determinants)

in order for people in Europe to buy these US bonds, they need to buy USD dollars. In order to buy USD they had to sell Euro. How do you think the USD has fared relative the Euro for 2019?( in theory how should it work? Appreciate? Depreciate?)