Bahrain is very concerned about Iran's nuclear ambitions.
Bahrain spoke to Israel about Iran's nuclear ambitions:
Bahraini Crown Prince Salman bin Hamad Al Khalifa, also the country’s prime minister, stressed to Israeli Prime Minister Benjamin Netanyahu “the importance of the participation of regional countries in any negotiations on the Iranian nuclear file” to support “security and stability in the region,” according to the official Bahrain News Agency.
One, Bahrain is worried that Iran Deal 2.0 will throw Iran's potential victims under the bus as the original 2015 deal did. So Bahrain doesn't want regional stability thrown away for even a real nuclear deal.
Two, a nuclear-armed Iran will have a shield to subvert or even invade Bahrain. Bahrain has a Shia majority ruled by a Sunni minority. Would Saudi Arabia intervene to save their ally if Iran had nukes to threaten Saudi Arabia with?
We'll see if the Abraham Accords created alliances that can withstand any Biden administration push to revive the Iran nuclear deal and so strengthen Iranian power and diplomacy (and eventually, nuclear capabilities).
