could add 4bn tonnes to US emissions by 2030

In what way does the graph indicate that? It's not raw emissions because that's around 5 billion, it's not change in emissions because that will be down from about 5.5 billion, it's not compared to Biden or his target because even Biden's target is only about 2 billion less.

The most generous interpretation I can give it is that they typoed 2050 in the title, and that it's Trump's ~4.2 billion rounded down vs Biden's target of 0. But even that's pretty wrong because that wouldn't be "adding" emissions, it would just be reducing emissions less.

Knowing how conservative these estimates tend to be, slope of the target should probably be waaaay higher.

I'm certain that there's extensive analysis on real data that prove the projections despite the lack of any real data (after we filter out the sad part)