The PM is trying to get the EU to revisit the Withdrawal Agreement by asking them to first strike out the 165 pages of the backstop. It is by no means clear Parliament would vote through the WA minus the backstop, as it still leaves us staying in the EU for another 21 to 45 months, paying them large sums, keeping us under the ECJ and various other undesirable features often discussed here. To a leaver the WA is not Brexit, and to a Remainer it is clearly worse than staying in. The PM would need to require other changes as well. The EU has repeated the mantra it put into the delay agreement, that it will not reopen the Withdrawal Agreement, so it looks as if there will be nothing to put to Parliament anyway. .