Tonight, the world will get the answer to a question that has been roiling global politics: is Donald Trump going to pull the US out of the Iran nuclear agreement?

The president has kept friends and enemies guessing but recent indications point to withdrawal.

Emmanuel Macron, the French president, left the White House in April concluding that “rational analysis” suggested Mr Trump would pull out. A senior European diplomat said this week it was "pretty obvious" Mr Trump would reimpose sanctions on Iran.

If the US does get out of the deal there a number of scenarios that could play out. Here are three of them:

Complete collapse

The decision that Mr Trump has to make by May 12 is whether or not to reimpose American sanctions on Iran.

The basic trade of the 2015 nuclear agreement was that the world would lift sanctions on Iran in return for Tehran agreeing to curb its nuclear weapons research. If Mr Trump puts those sanctions back into place he has effectively reneged on America’s side of the bargain.