The structure is analogous to "That made the teacher happy", which I expect you can understand OK. Instead of the noun "teacher", you have the noun phrase "flawed opening". Instead of the adjective "happy", you have the adjectival phrase "all the more disappointing ...
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Anonymous"That made the flawed opening all the more disappointing to supporters of the health plan, including ..."In the grammar I am familiar with, opening is a noun in your sentence, not a gerund. This is because it is modified by the. Opening is also included in dictionaries as a noun.