We've all heard about the insurers that are pulling out of Affordable Care Act marketplaces, but sometimes you have to see it to really get it. This map is based on data from the Kaiser Family Foundation for the first four years of the ACA marketplaces. You can really see the difference in 2017, when high-profile insurance exits left 21 percent of all ACA customers with only one insurer in their area.

Expand chart Data: Kaiser Family Foundation; Map: Lazaro Gamio / Axios

For context: This doesn't even count 2018, when there could be as many as 47 counties with no insurer at all. We'll have a better idea after this week's filing deadline, of course.

Why it matters: There are definite signs that the Trump administration's opposition to the ACA is hurting the marketplace for next year, as we wrote on Friday. But it's important to remember what was happening before the administration ever took office.