Since this insanity has been grinding away for nearly seven years now, I'm pretty much just reposting my entire August entry, with an important update tacked on at the end.
Here's a quick recap:
The ACA includes two types of financial subsidies for individual market enrollees through the ACA exchanges (HealthCare.Gov, CoveredCA.com, etc). One program is called Advance Premium Tax Credits (APTC), which reduces monthly premiums for low- and moderate-income. APTCs are the subsidies which have been substantially beefed up by the American Rescue Plan (the additional subsidies will be available starting in April in most states, soon thereafter in most other states).
The other type of subsidies are called Cost Sharing Reductions (CSR), which reduce deductibles, co-pays and other out-of-pocket expenses for low-income enrollees.
In 2014, then-Speaker of the House John Boehner filed a lawsuit on behalf of Congressional Republicans against the Obama Administration. They had several beefs with the ACA (shocker!), including a claim that the CSR payments were unconstitutional because they weren't explicitly appropriated by Congress in the text of the Affordable Care Act (even though the program itself was described in detail, including the payment mechanism/etc.)