Comprehensive immigration reform could make millions of people suddenly eligible for assistance under President Obama's healthcare law, assuming a final deal paves the way for undocumented immigrants to receive papers. Illegal aliens are now prohibited from purchasing coverage through the Affordable Care Act's insurance exchanges, which will launch next year. They are also ineligible for Medicaid under most circumstances, making the law's expansion of the program fruitless for people without documents. Even young illegal immigrants with "deferred action" status, known as "DREAMers," cannot access the law's benefits. But the picture could change completely if Hispanic lawmakers get their wish —...