WASHINGTON — When he talks to Republicans in Congress, Scott DeFife, a restaurant industry lobbyist, speaks their language: President Obama’s health care law is a train wreck well down the track. There will be collateral damage if changes are not made. Friends of the industry cannot sit back and let that happen.

Speaking to Democrats, he puts on his empathy hat: The Affordable Care Act is the law of the land. Its goal of universal insurance coverage is laudable, but its unintended consequences will hurt the cause.

Almost no law as sprawling and consequential as the Affordable Care Act has passed without changes — significant structural changes or routine tweaks known as “technical corrections” — in subsequent months and years. The Children’s Health Insurance Program, for example, was fixed in the first months after its passage in 1997.

But as they prowl Capitol Hill, business lobbyists like Mr. DeFife, health care providers and others seeking changes are finding, to their dismay, that in a polarized Congress, accomplishing them has become all but impossible.