If the US government nationalizes anything, it's going to run approximately as well as NASA - bloated, expensive, slow, lacking focus. Engineers who want to work on his projects don't have to work in their home countries if the projects are domiciled somewhere else. If Musk simply stops doing what he does, everyone loses whatever he might have done. (A few people are fond of "he didn't actually build all of that himself" rhetoric. No, he didn't, but he put it all together, whereas no-one else had done so.) If Musk keeps on doing what he does in spite of confiscation and, possibly, criminal prosecution, I doubt he's going to roll over and accept what Democrats do to him; he'll move.
[Add: "SpaceX is on US government dole" is one frame. "US government is critically dependent on SpaceX" is another.]