When the bond matured, you need to pay back the money. 1, America do not have that USD900B in cash 2, America has to find other buyers for their USD900B bond, who? If nobody wants to buy, then they have offer higher coupon rate(interest). 3, the prevailing interest rate is likely still much higher than few years ago, so if interest rate stays high as Powell refused to bow to Trump's pressure, America has to sell the bond at much higher interest rate and high interest rate is a killer to the federal government. If they can't pay, the US government have to stop operating, not paying the civil servants or raise the debt ceiling forever...
That's why the Chinese analyst should be right that, this is Trump's effort to save America government from bankruptcy... though overdone... At least he should not done it to allies and foes... Or perhaps he calculated that even all his foes add together are not enough to save America and thus he roped in allies for this tariff war and it's back firing now?
And if you read his demand for the tariffs, there is only one conclusion. He needs money, lots and lots of money!