Unfortunately, you're still operating in the land of norms. We don't know, he's moving so fast and breaking so many laws and gutting so many institutions and making so many threats and ideas that we just cannot keep up.
At this point, your assumption of even having elections in 2028 could be faulty. Remember, there was an attempt overthrow the US government in 2021 by Trump.
But to answer your question: he can basically do anything he wants and the only thing that could stop him is mass refusals or the Republicans in legislation. There is nothing else.
> your assumption of even having elections in 2028 could be faulty.
The 2026 midterms will likely be compromised too. Remember that Trump has pardoned all J6 rioters. One can now expect more hardcore MAGA folks to come out of the woodwork to destroy voting booths in Democrat-leaning constituencies, knowing that they won't suffer any consequences.
At this point, your assumption of even having elections in 2028 could be faulty. Remember, there was an attempt overthrow the US government in 2021 by Trump.
But to answer your question: he can basically do anything he wants and the only thing that could stop him is mass refusals or the Republicans in legislation. There is nothing else.