President-elect Donald J. Trump will encounter an Iran that is suddenly far more brittle than it was during his first administration, its leadership more uncertain, its nuclear program more exposed and vulnerable to attack.

That new reality has touched off an internal debate about how his administration should approach Tehran: with an openness to negotiations, or with an attack on its nuclear enrichment program — overt or covert, or perhaps initiated by Israel.

Or, as many suggest, a round of “coercive diplomacy” that leaves Tehran to choose either a negotiated disassembly of its nuclear capability, or a forced one.

The urgency of the issue was underscored on Sunday by Jake Sullivan, President Biden’s national security adviser, who told Fareed Zakaria of CNN that with Iran’s main proxies weakened or eliminated, “it’s no wonder there are voices saying ‘Hey, maybe we need to go for a nuclear weapon right now.’”

He added that he had discussed the “real risk” of an Iranian race for the bomb with the Trump national security team and with the Israelis.

In interviews over the past two weeks, American and foreign officials have said that the menacing dance over Iran’s nuclear future could take a dramatic turn in the next few months. That assessment came after the U.N.’s top nuclear inspector warned that Iran was accelerating its enrichment of near-bomb-grade uranium.