In a national vote widely viewed as a victory for conservatives, last year’s elections also yielded a win for liberals in eight states that legalized marijuana for medical or recreational use. But the growing industry is facing a federal crackdown under Attorney General Jeff Sessions, who has compared cannabis to heroin.

A task force Mr. Sessions appointed to, in part, review links between violent crimes and marijuana is scheduled to release its findings by the end of the month. But he has already asked Senate leaders to roll back rules that block the Justice Department from bypassing state laws to enforce a federal ban on medical marijuana.

That has pitted the attorney general against members of Congress across the political spectrum — from Senator Rand Paul, Republican of Kentucky, to Senator Cory Booker, Democrat of New Jersey — who are determined to defend states’ rights and provide some certainty for the multibillion-dollar pot industry.

“Our attorney general is giving everyone whiplash by trying to take us back to the 1960s,” said Representative Jared Huffman, Democrat of California, whose district includes the so-called Emerald Triangle that produces much of America’s marijuana.