Theresa May’s attempts to renegotiate the backstop have been met with a sharp rejection from European member states and the European Commission. (In other news, you won’t believe what bears get up to in the woods!)
The PM is seeking a logical impossibility: the point of the backstop is to provide a guarantee that, regardless of what happens in the talks, there will not be a hard border on the island of Ireland. That means that it cannot, by definition, be time-limited or have a unilateral right of exit for the United Kingdom.
The Irish government has a veto on the terms of the final trade agreement, and no Irish Taoiseach could sign a trade deal that puts a hard border on the island of Ireland – the economic damage of no deal will always be a better proposition than the political damage of that deal whichever party is in office in Ireland.
But Conservative opponents of the backstop will never accept a deal that keeps the United Kingdom within the regulatory orbit of the European Union indefinitely. That means that the only way to pass the withdrawal agreement is to soften Brexit to get support from other parties, something May has no inclination to do, or to offer a second referendum. But no one should rule out the possibility that the United Kingdom ends up with a no-deal exit instead.