As long as "Obamacare" remains intact -- or the Democrats gain power and improve it -- elder immigrants can get insured. Prior to "Obamacare" the medical situation was really dreadful for elder immigrants, among others.
Let's suppose you're a 70 year old male Singaporean, you're not U.S. Medicare eligible, but you're married to a U.S. citizen or U.S. permanent resident and go live with your spouse in Miami. You can obtain an "Obamacare" medical insurance policy via Healthcare.gov (the U.S. federal exchange), and there are no preexisting condition exclusions....
....But it is not cheap. The lowest cost plan, assuming you don't qualify for tax subsidies (your income is "too high"), is US$780/month (2019). There's a US$7,900 annual deductible, so you pay that amount first for your medical care. And you're limited to a "network" of medical providers (doctors, hospitals, clinics, etc.) -- you cannot obtain care from every provider.
....But it is excellent. Above the deductible, and within the network, the coverage is very, very comprehensive. Virtually all acute care is covered without any additional expense for the amount above the annual deductible, including prescription drugs and even emergency care outside the United States.
Once you've clocked 5 years of U.S. residence, and if your spouse is U.S. Medicare eligible, you should be able to enroll in Medicare. That'll be more affordable than the exchange policy, and if it's a "Medicare Advantage" plan it should provide still comprehensive coverage (without a provider network) but with much lower out-of-pocket costs.
Where you can really rapidly run down assets is with long-term care, which is also quite expensive in the United States. You can usually get LTC insurance, but it too is rather expensive.
Anyway, there are solutions available if you can get past the significant immigration restrictions, but as always (with every retirement destination) you have to do some careful research and budgeting.
780 USD a month is 13k sgd premium a year, and its the lowest cost plan.
My integrated shield plan fully covered my 3 day stay in B1 ward and it only cost me a few hundred dollars premium a year.