Few seem to grasp this point. There are still portions of the EU from which the UK must detach itself. The EU will not wish them to do so and you can bet that they will 'play hardball' using this as leverage in negotiations.
At the same time, they will do their level best to make negotiations stretch well beyond 2020.
The talks will not be amicable as the Eurocrats move in to punish the UK as a warning to any other nations wanting to quit The Evil Empire.
Assuming a Boris win (Heaven help us if he has no overall majority) - he can probably still engineer some sort of 'no deal' using WTO rules which is a mighty bargaining chip and should put Brussels firmly in its place if he shows sufficient bottle.
Having already achieved his mediocre first step - there can be no real plaudits for BoJo. That can only come about if he detaches us from: EU conventions; threats to our fishing industry; the ECJ etc, by refusing to kowtow to Brussels where the Political Declaration is concerned.
None of the above would have been remotely possible under Theresa May's Chequers plan.