Why is Trump risking a 'forever war' with Iran?

Rip up the Memorandum of Understanding, the ceasefire is well and truly over. Iran and the United States are once more at war – with oil tankers targeted and the Strait of Hormuz firmly shut.Donald Trump's response? He insists the US will take control of the disputed waterway and act as a "guardian angel" for all ships passing through.Originally, he wanted to charge a 20% toll for the privilege, before backtracking on what seemed like an unworkable claim.But is the US still in danger of being dragged deeper into a long-term conflict with Iran that could have repercussions for the region – and the global economy – for years to come?Niall Paterson is joined by Sky's military analyst Professor Michael Clarke.