To some degree, yes - Massachusetts did that, in fact, and the plan there (that was signed, somewhat ironically, by Mitt Romney) is very very similar to the ACA

To some degree, yes - Massachusetts did that, in fact, and the plan there (that was signed, somewhat ironically, by Mitt Romney) is very very similar to the ACA. There are a lot of details, though, that make this complicated and not necessarily viable for all states (MA is both relatively wealthy, has relatively wealthy neighboring states, and has a somewhat unusual healthcare market).