LONDON — America and Iran took a step toward a final nuclear deal on Jan. 18, but they should be making leaps. The negotiators have proposed some creative solutions but major political compromises are sorely needed, and soon.

If a framework agreement can’t be reached in March, the talks could become mired in stalemate. Those who oppose any diplomacy between Iran and the West are already seeking to end the process altogether. With time, they will gain further ammunition.

Spoilers have been striking from Tehran, Washington and Tel Aviv. Some are trying to limit the ability of President Barack Obama (or whoever succeeds him) to deliver a reasonable sanctions-relief package to Iran. Others are seeking to corner Iran and force its government into knee-jerk reactions to regional flare-ups. Hard-liners in the United States and Iran see the nuclear negotiations as an opportunity to score points domestically and they are escalating their efforts to scuttle a grand bargain.

Although the Obama administration has dedicated itself to multilateral diplomacy with Iran, it has been under constant pressure from Congress. Powerful American legislators, influential lobby groups and the Israeli prime minister have repeatedly called for increased economic pressure on Iran to extract further concessions. Not only does this contradict America’s interest in maintaining the freeze on Iran’s nuclear program, but it also devalues the agreement brokered between Iran and France, Britain, Russia, China, America and Germany.