'I don’t really see how they can maintain the reserve currency without running trade deficits.'

It is rather easy. USD as the primary reserve currency means there is demand for USD for use in trade payments and as a SoV, often held by preference as USTs. While nations selling goods to the US gets them USDs that is not the only way they can access USD. US can issue USD in exchange for investments in other countries and as loans. It has always done this, but the demand for USTs was so strong it was easier to issue them than to make investments. The whole petrodollar paradigm was built upon giving the Saudis preferential access to USTs and then others wanted access as well. It became all too easy, rather than the trouble of managing investments you just issue debt obligations. Other nations and entities can access USD as a SoV in the form of USD denominated investments...but again, they preferred USTs and the US issued them. It was not essential, but a choice. A choice that has led to the current situation where USTs and other US government debt now impose a burden of debt servicing greater than the cost of maintaining the military. Reckless. The truth is that the demand for USTs has enabled the US government to easily fund seemingly endless fiscal deficits and this lack of fiscal discipline is now delivering the inconvenient reality of imminent insolvency. There was no functional need for the US to become hugely in debt in order to operate the primary global reserve currency- but rather it has turned out that way because there has been a chronic lack of discipline and an erroneous belief that the accumulation of debt could continue without any serious consequence.