Obamacare was destined to fail, regardless of whether Donald Trump expedited the process or not. The ACA's shortcomings can be traced to the implementation and parameters of its Shared Responsibility Payment (SRP).
The SRP is Obamacare's "penalty" for not purchasing health insurance, and it was put in place by lawmakers in order to coerce healthier young adults to enroll. These young adults are a vital component to the ACA's success because of the other mandates attached to the law's passage -- namely, that insurers are required to accept all applicants, regardless of whether they have pre-existing conditions, and are not able to charge them more because of their pre-existing conditions. This pushed medical expenses for health-benefit providers way up. Therefore, the monthly premiums of healthier young adults who were unlikely to head to the doctor much were needed to offset this adverse selection (i.e., the initial uptick in sicker-patient enrollment). Motley Fool