There is literally nothing any President going forward can promise without Congress completely having the President's back or the Justices agreeing with the President.

This was always true. The Affordable Care Act was met with repeated judicial challenges and survived thanks to judicial interpretation.

Regulatory rules have alsp always been subject to judicial review, especially after the public comment period. If an agency does not respond to comments, a rule can be struck down as arbitrary.

The difference now is that the courts can evaluate rules not based on scientific and administrative expertise but on ~~ideology~~ whether they adhere to the legal authority Congress granted them. Chevron deference implied that Congress gave agencies the legal authority to adapt to new situations. The misanthropes of the Supreme Court disagree because, for them, the Constitution is a dead document allowing adaptation to anything at all.