By Anna Wilde Mathews and Paul Overberg | Graphics by Elizaveta Galkina

As Congress gears up to pass President Trump’s massive legislative package, one of the biggest fights is over the future of Medicaid. To make their targeted budget numbers, Republicans will likely need to carve hundreds of billions of dollars in spending out of the health program that serves lower-income people. But Medicaid is a political flashpoint because of the core role it plays in the lives of millions of Americans—many of whom vote for Republicans—as well as state budgets and the healthcare economy.

Here’s why the stakes are so high as lawmakers debate its future.