One of the reasons that Obamacare was an unmitigated failure was how they implemented pre existing conditions. Under Obamacare, you could buy your medical insurance when you needed it, as they were wheeling you into the ER on a gurney. This drove the price of health insurance through the roof. In order to offer no pre existing conditions, you have to spread the risk to everyone and everyone has to carry coverage as you must do with automobile insurance.
That's not a pre-existing condition as defined by the insurance industry. If you have cancer and lose your health insurance and have to find a replacement, the new company can refuse to cover your cancer costs because they had been diagnosed before you asked them to cover the costs. That's what most people think about when they talk about pre-existing condition coverage and that's what scares the heck out of people.