Since I don't think I could convince you that any phase of a state free-for-all to stop abortion would be "bad", I'll skip that and instead talk about Trump's deportation plan.
The first part is that he's not talking about the ones "Biden let in". Trump is planning the deportation of *all* "illegals" inside the US. This amounts to over 10 million people. The costs would be enormous.
How do you find and remove 10 million people inside our country? Well Trump plans to use the military, particularly the National Guard. This is a problem for several reasons. First, the National Guard works for the states, not the President. Second, use of the military for police work is explicitly forbidden by federal law (Posse Comitatus Act). Third, from a more practical view, the national guard has no experience doing police work.
Our economy has modest growth (a couple percent), mildly high inflation (4-5% annual, versus 2-3% for the prior decade), and low unemployment. The economy may not be perfect, but any "worsening" isn't all severe and is not tied temporally to changes in migration. (The causes are pretty clear and are largely tied to the aftershocks of the pandemic.)
The "illegals" include a large number of workers. That is the primary reason people come here illegally. Some do bring small children, but we are mostly talking about deporting workers. (There are no social services from the government for them.)
A mass deportation will remove millions of workers from the economy who not only do work, but spend money. There would be a severe labor shortage, especially in some areas where large numbers of undocumented workers work.
I'm sure some other fascist will wrest it from him. That's they way they work.
