It doesn't directly impact the dollar, per se, but it does mean that the government has to find the money elsewhere to continue operations. If it has to look harder, it will have to spend more, and that ultimately has to be backed by the taxpayer.
The key thing here isn't about the reserves, its how they they acquired them by creating a swap on USDCNY from Chinese exports from their reserves - effectively holding the Yuan from appreciation.
The other thing is for the trade deficit to decrease the reserves need to decrease too. The reserves, especially the way they were created using swaps give a proxy of USD held savings held but not yet poured back into the US (and hence creating a trade deficit).
This is all of course useless if the holder of those bonds is still China, but through another country such as Belgium with an overseas account - which they've done before.
It's ideal for all US debt to be held domestically if only to remove this constant absurdity that people fall for, the propaganda that China (or the Saudis et al) could do anything to injure the US using their very modest treasury holdings.
So far the US hasn't actually done anything drastic with tariffs, even with regards to China. Mostly what Trump has done is use it as a bluff to get concessions, and that's mostly all that he will do. China may be the exception, as necessary. That may be warranted, the US should match China's barriers if China doesn't start opening up fair access & treatment re their economy.