What could Iran do if Trump pulls out of nuclear deal?

Tehran: US President Donald Trump will announce on Tuesday whether his administration will withdraw from the Iran nuclear deal. Tehran signed the Joint Comprehensive Plan of Action, with China, France, Germany, Russia, Britain and the United States in 2015.
Iran agreed to curbs on its nuclear programme in exchange for the lifting of some sanctions. But the withdrawal of the United States would probably sink the deal. If that happens, Iran could retaliate by undermining the interests of Washington and its allies in the Middle East.
Here are some possible scenarios, should Trump pull the US out of the deal:
Iraq
When Daesh seized much of Iraq in 2014, Iran was quick to support Baghdad. Iran has since helped arm and train thousands of Shia fighters in Iraq. These Popular Mobilisation Forces (PMF) are also a significant political force.
If the deal falls through, Iran could encourage PMF factions who want the US to leave Iraq to step up rhetorical, and maybe military, attacks against American forces.
These could be rocket, mortar and roadside bomb attacks not directly linked to a specific Shia militia, which would allow Iran to deny it had changed its position of avoiding direct conflict with US forces in Iraq.
Syria
Iran and paramilitary allies such as Lebanon’s Hezbollah have been involved in Syria’s war since 2012. Iran has armed and trained thousands of Shia paramilitary fighters to shore up the government. Israel says Iran has recruited at least 80,000 Shia fighters.
Iran’s presence in Syria has brought Tehran into direct conflict with Israel for the first time, with a series of high-profile clashes in recent months. Israeli officials say they will never let Tehran or Hezbollah establish a permanent military presence in neighbouring Syria.
If the nuclear deal falls through, Iran will have little incentive to stop its Shia militia allies in Syria from carrying out attacks against Israel.
Iran and the forces it controls in Syria could also cause trouble for about 2,000 US troops deployed in northern and eastern Syria to support the YPG-dominated Syrian Democratic Forces (SDF).
A top adviser to Iran’s Supreme Leader said in April he hoped Syria and its allies would drive US troops out of eastern Syria.
Lebanon
In 2006, Hezbollah fought Israel to a standstill in a 34-day border war. According to Israeli and US officials, Iran is now helping Hezbollah build factories to manufacture precision-guided missiles or refit longer-range missiles with precision guidance systems.
Israeli forces have repeatedly attacked Hezbollah in Syria where the group is leading many of Iran’s Shia militia allies. The rhetoric between Israel and Iran has ramped up in recent weeks. Though Hezbollah and Israel say they are not interested in conflict, the tensions could easily spill over into another Lebanon war.
Hezbollah said last year that any war waged by Israel against Syria and Lebanon could draw thousands of fighters from countries including Iran and Iraq, indicating that Shia militias could come to Lebanon to help Hezbollah.
Hezbollah and its political allies won just over half the seats in Lebanon’s parliamentary election, unofficial results showed on Monday. For the moment, the group is working with its political opponents.