The assassination of Iran's top nuclear scientist may also prove lethal to President-elect Joe Biden's stated desire to recommit to the Iran nuclear deal.

Whether that was the objective of Friday's killing of Mohsen Fakhrizadeh is unknown. What is clear is that the reaction from adversary and ally alike may make it more difficult for the U.S. to diplomatically re-engage with Iran and return to the multinational pact that was negotiated during the Obama administration.

President Donald Trump reneged and withdrew America from the deal in 2018 and subsequently leveled severe sanctions on Iran for its malign regional activities. The accord was also opposed by Iran's Middle East adversaries. That includes Saudi Arabia, which is part of a broader regional split between majority Sunni, Arab nations and Persian, Shiite Iran.

Iran accused Israel of being behind the slaying, which seems certain to embolden Iranian hard-liners. They already were deeply skeptical, if not outright opposed, to the deal with the U.S. and other world powers that was intended to curb Iran's potential nuclear weapons program.

By nearly every account, including the Trump administration's, Iran lived up to the nuclear compliance portion of the deal during the time that the U.S. was still party to it. But now, it is not. And the theocracy has also continued its destabilizing and deadly support of proxies in countries such as Lebanon, Syria, Iraq and Yemen.

Iran's extremists may be emboldened not just by the recent events but by the run-up to the country's June's presidential election. "Iranian politics now is completely about the upcoming elections, and no one wants to look weak," Patrick Clawson, a senior fellow at the Washington Institute of Near East Policy, told an editorial writer.

The ostensibly more moderate Iranian factions may try to wait until Biden is president in order to press for a U.S. return to the deal. But hard-liners may move sooner in advocating an attack to avenge Fakhrizadeh's killing. If so, it could create an escalatory spiral just as the U.S. is speeding its withdrawal of forces in Afghanistan and Iraq and as the more rhetorically bellicose Trump administration transitions to an incoming Biden administration that has designs on diplomacy — an already fraught process that will be much more challenging that when the original deal was inked in 2015.

"It's going to be complicated and difficult negotiations; it's not going to be, 'We're back,'" Clawson said.

Ultimately, the goal is to stop Iran from having the capacity to develop a nuclear arsenal. And while the assassination of a scientist will have Iranians, in Clawson's words, "tied up in counterintelligence knots," it doesn't totally void Iran's institutional knowledge of nuclear proliferation processes.

Multilateral diplomacy was and remains the best way to stop Iran from developing a weapon and triggering a dangerous regional proliferation race. Biden is right to want to work with world powers to do this. But given Iranian intransigence, as well as the significant shifts in Mideast politics since Biden left office in 2017, it won't be easy.