Joe Biden has readily imposed sanctions against U.S. adversaries throughout his presidency. Now he’s finding out that lifting them is a lot harder.

In recent months, as Biden has mulled reducing such penalties against countries such as Venezuela and Iran, he’s run headlong into opposition in Congress. Some lawmakers, knowing the topic will play well on the campaign trial, vow to do everything they can to stop the sanctions from being lifted.

It’s the type of drawn-out political fight that could make U.S. sanctions less effective over time if adversaries come to believe that, no matter what they do, Washington will never lift penalties on them. It’s playing out as the United States, determined to limit its military exposure abroad, has grown more reliant on sanctions, including against Russia.

“U.S. politics constrains our ability to provide sanctions relief, even when the executive branch wants it,” said Edward Fishman, a former State Department official who helped craft sanctions strategy for the Obama administration. “The on switch is much easier to press than the off switch.”

Venezuelan President Nicol?s Maduro gestures as he speaks during a press conference at Miraflores Palace on Feb. 17, 2021, in Caracas, Venezuela.