Two obvious ones have gotten much attention:  Pete Hegseth for Defense Secretary, and Kash Patel for FBI Director.  Both evince a fascistic or authoritarian temperament and ambitions.  Putting either in charge of people with guns and authorized violence would be very dangerous in the extreme.  Ironically, as of this writing, Hegseth seems likely to be rejected not for being a Christian nationalist and authoritarian, but for being a sexist and a drunk.  I'll take that if that's the reason.  That may allow attention to shift to Patel, who is quite unhinged.

At least as dangerous, but in a different way, is the prospect of an ignoramus like RFK Jr. becoming Secretary of Health & Human Services.  Public health is the kind of social good it's easy to take for granted, until it's gone.  RFK will accelerate declining uptake for vaccines, and promises to direct research funding away from infection diseases–God forbid there's another pandemic.  Fortunately–at least for those in civilized states–the states still set legal requirements for mandatory vaccinations, but even if Illinois has 21st-century public health policies, it will be a problem if neighboring Missouri or Iowa do not.  Viruses don't respect state lines.

Unless the U.S. is very lucky, the next four years could see massive outbreaks of infectious disease, with no coherent federal response; political arrests and prosecutions (maybe murders?); and a politicized military occupying Democratic cities in search of immigrants and "preserving law and order."