Why is Trump against the Iran nuclear deal?

This is a last chance. That is the message US President Donald Trump has sent out after extending sanctions relief to Iran.

He has aggressively warned European allies he would withdraw from the 2015 nuclear agreement altogether, if his demands to change it are not met.

Trump has publicly branded the deal before and during his presidency as the 'worst ever'.

Iran says his announcement is a 'desperate attempt to undermine a solid multilateral agreement' that is not 'renegotiable'.

In the middle of all of this are European leaders who have essentially said to Trump: either back the deal or come up with a better one.

But can this deal be re-negotiated?