The US is big enough that it doesn’t need to trade. It could easily sustain itself as a closed economy. The reason the US trades with other economies is that it benefits from trade. The benefits are diverse, but the biggest economic factor is that trade allows the US to send low-value economic activity overseas, and concentrate on high-value economic activity. If the gain from concentrating on the high-value activity is greater than the amount paid overseas for the low-value activity, then the US wins from trade, even if it’s buying more low-value activity than it’s selling high-value activity.
The first caveat to the above paragraph, is that when the US pays for low-value activity, it’s not paying directly with high-value activity but with wealth. So if overall wealth is increasing due to the gain mentioned above, the payments out don’t matter. However, if outward payments are greater than the internal gains, then the US is losing wealth. A long-term prolonged loss of wealth will eventually result in a shrinking economy, and the greater the wealth loss before the tipping point is hit, the severer the impact.
The second caveat is that net economic gain isn’t uniform across the country. So, for example, the US software industry has undoubtedly been doing well, but bicycle manufacturing hasn’t (https://aushiker.com/where-was-my-bicycle-made/ ). If the gains are concentrated, but the losses are dispersed, then there could be an average gain, but a median loss. In other words, it’s possible that the winners are doing well, but there are more losers than winners. That also has long-term implications that will eventually result in a shrinking economy.