The world is waiting to see whether Iran will strike back at Israel or the U.S. over the assassination of Mohsen Fakhrizadeh, the architect of Iran's military nuclear program.

Why it matters: Senior Iranian officials have stressed that Iran will take revenge against the perpetrators, but also respond by continuing Fakhrizadeh’s legacy — the nuclear program. The key question is whether Iran will accelerate that work now, or wait to see what President-elect Biden puts on the table.

The backstory: Iran has waited out two years of "maximum pressure" under President Trump, breaching the enrichment limits of the 2015 nuclear deal after Trump withdrew but stopping short of more drastic steps.

• Biden has long said that if Iran returns to compliance, he'll loosen sanctions in order to bring the U.S. back into the deal.

State of play: Hardliners in Tehran have long been critical of President Hassan Rouhani's "strategic patience" policy, and their voices have grown louder in the wake of Fakhrizadeh's assassination.

• Parliament passed a non-binding resolution on Tuesday calling on the government to raise uranium enrichment levels to 20%, start rebuilding the heavy water reactor in Arak, and limit the access of UN inspectors to Iran's nuclear sites.

The other side: The more pragmatic camp, led by Rouhani, argues that such steps on the nuclear program would play into the hands of the Trump administration and Israel.

• They stress the need to prioritize the removal of U.S. sanctions once Biden assumes office — a goal they think is at hand.
• The decision is ultimately in the hands of Supreme Leader Ali Khamenei. His public comments thus far have not indicated that he's siding with those arguing for an imminent acceleration on the nuclear front.

The latest: Biden and his transition team have been silent on Fakhrizadeh's assassination, and several Biden aides refused to comment on the matter for this story.

Flashback: The two-tiered debate over Iran's response echoes the aftermath of the killing of Gen. Qasem Soleimani, the commander of the Quds Force, by the U.S.

• Iran took tactical revenge by launching missiles at American bases in Iraq. But Iran's strategic response was to press the Iraqi government to call on the U.S. to pull its troops out of the country.

What to watch: Diplomats from world powers who are still part of the nuclear deal (Russia, China, France, Germany, the UK and the EU) will meet Iranian officials in Vienna on Dec. 16 to discuss ways to preserve the deal, get Iran back to full compliance and prepare for the new U.S. administration.