There are four basic ways to get health care coverage (there are also some very minor exceptions to these that impact far fewew people):
- You can be eligible for Medicaid.
- You can be eligible for Medicare.
- You can buy private health insurance in the ACA exchange market for your household (and you are required to due so under penalty of paying a fine under the ACA).
- You can receive private health insurance through an employer who in turn buys an employer group health insurance policy in a (figurative) employer group health insurance market that is separate and distinct from the ACA exchange market.
As used here "you" usually operates on a household basis that includes you, your spouse, your minor children and your young adult children.
Your question addresses options 3 and 4.
With respect to option 3:
The far bigger concern is that a county have zero insurers, because the ACA does not address how to deal with that possibility.
The problem with a county having only one insurer is that the ACA individual exchange market relies primarily on competition to bring about reasonable premiums for policies offered on the exchange (and the premium for Bronze plans is also used to set subsidy levels under the ACA for participants in the individual exchange market). If there is only one insurer in a county it can set any premium it wishes, anyone in that county who wants an individual exchange market plan in that county has to pay it, and the price of that plan will determine the ACA subsidy amount for that plan.
With respect to option 4:
Am I correct (based on my limited experience) that most, if not all
employer- sponsored health insurers offer only one insurer ? And if
this is correct, why are US politicians alarmed that there could only
be 1 insurer participating on the ACA exchange in certain counties
Not all employer based health insurance plans offer only one insurer. Indeed, in big businesses and large government agencies, the norm is for more than one health insurance plan to be available for an employee to choose from, and employer based plans involving multiple choices are probably at or close to a majority of all employer based health insurance plans by number of employees covered.
But, most smaller employers offer only one health insurance plan for their employees.
This is still not a problem, because employer-sponsored health insurers are chosen by employers who are price conscious, from multiple available employer group health insurance plans available in the employer group health insurance plan market.
There is not a shortage of companies offering plans in the employer group health insurance plan market in most places. This is (1) because the employer group health insurance market is bigger as a share of the total private health insurance market, (2) because it is more profitable since one marketing sale to an employer results in the sale of health insurance to multiple households for a larger total premium and (3) because it is more profitable since there are fewer opportunities for adverse selection and moral hazards by prospective insureds in the employer group health insurance plan market in a world where lots of people required to get individual health insurance plans fail to do so except when they think they will need to purchase expensive health care.
In the case of employer group health insurance plans, the purchasing decision is just made at the employer level rather than the employee level. But, since employers usually pay a significant share of the premium for an employer based group health insurance plan, they have a strong incentive to choose a health insurance plan that provides good benefits relative to the premium charged vis-a-vis other employer based group health insurance plans competing for their business in the same marketplace. Therefore, the competitive marketplace still provides a market based means to regulate health insurance premiums.