Cruz and Rubio haven’t said yet that they will go quite that far:
This is a radical change compared to the 1970s when Richard Nixon and his EPA director William Ruckelshaus were in the forefront of environmental protection.
Turning regulation back to the states allows lots of options for states to tell industry: “If you bring your manufacturing plant to our state you don’t need to worry about any pesky environmental regulations.”
It is a very different GOP from Nixon’s time–and while it’d be fun to think this is just another crazy thing Trump says, this actually isn’t necessarily out of the GOP mainstream. As far back as 4-5 years ago there were attempts by Tea Party Republicans in the House to try and get the EPA abolished legislatively (I don’t think it ever made it to a floor vote, but I’d have to check on that.) Unfortunately this is right in the wheelhouse of something that a sizable number of Federal elected officials in the Republican party would find acceptable.