The sudden uncertainty surrounding the future of the Affordable Care Act could be an enormous political liability for Republicans in key states come November.

Between the lines: Millions of people in crucial presidential and Senate battlegrounds would lose their health care coverage if the Supreme Court strikes down the law, as the Trump administration is urging it to.

The chart above shows the number of people enrolled in the ACA's insurance marketplaces or covered through its Medicaid expansion.

• These options have become especially important over the last six months, as millions of Americans lost their jobs — and thus their employer insurance — due to the pandemic.
• And more than a quarter of non-elderly Americans have a pre-existing condition that insurers in the individual market could refuse to cover without the ACA, per the Kaiser Family Foundation.

The big picture: Republicans paid a steep electoral price for trying to repeal parts of the ACA in 2017. Republicans' lawsuit against the health care law, if it succeeds, would boot even more people off of their coverage and undo even more of the ACA's regulations.

What to watch: Several vulnerable Republicans, including Sens. Susan Collins, Martha McSally, and Cory Gardner,, represent purple states that expanded Medicaid and would therefore see steep coverage losses. And the broader fight over the Supreme Court has made it impossible to ignore those stakes.

• "With the Court setting Nov 10 as the date for hearing California v. Texas, Republicans caught a break not having it front and center right before the election.  Now it is very much front and center," said Rodney Whitlock, a former health aide for Sen. Chuck Grassley.
• "Debates over protection of pre-existing conditions have generally not gone positively for Republicans in purple states/district," he added.