They could not do it, despite their best endeavours.

他们尽了最大的努力，但还是做不成功。

Despite our best endeavours, we couldn’t start the car.

【endeavour】我们虽然尽了最大努力，但还是无法发动汽车。

They committed that in such an event, the EU would use their best endeavours to continue to negotiate and conclude as soon as possible a subsequent agreement that would replace the backstop.

他们承诺，在这种情况下，欧盟将尽最大努力继续协商，并尽快缔结一项取代保障协议的协定。