A bipartisan group of senators wrote a letter to US President Joe Biden on Thursday, urging him to pursue a diplomatic strategy to prevent Iran from obtaining a nuclear weapon. Their language indicates possible congressional support for a new, more comprehensive agreement with Iran in place of the 2015 nuclear deal, but such a deal could run into opposition from Iran and US progressives.

The 43 senators began by saying that Iran obtaining a nuclear weapon would pose a “grave threat” to the United States. Iran insists its nuclear program is for peaceful purposes, but critics in the United States, Israel, the Gulf and elsewhere allege Iran seeks to build a nuclear bomb. The senators also said that Iran’s missile program and attacks by Iran-backed militias in Iraq on the US military constitute further threats, referring to the latter as “Shia militias.”

Democratic Sen. Bob Menendez of New Jersey and Republican Sen. Lindsey Graham of South Carolina led the signing of the letter, according to a Senate Foreign Relations Committee press release. Menendez heads the committee.

To this end, the senators urged the Biden administration to enter into an agreement that restricts both Iran’s nuclear program and its other defense and regional policies.