(Bloomberg) — Boris Johnson is giving members of Parliament only a few days to debate the most important change to Britain’s constitution in almost 50 years. The outcome will decide the fate of Brexit and potentially his own future.Unlike his predecessor, Theresa May, the prime minister wants Britain to have far looser ties with the European Union after leaving, which means withdrawing in full from the bloc’s customs union. That decision may have helped him to pacify the Tory right, which torpedoed May’s proposals three times, but it leaves him facing opposition on multiple fronts. The opposition Labour party, for starters, wants to remain in the EU customs union.With the voting in Parliament on whether to back his deal too close to call, here are some of the key issues that Johnson has to navigate.Northern IrelandThe Democratic Unionist Party has refused to back his deal because it would see Northern Ireland being treated differently for customs purposes to the rest of the U.K. The grouping is also unhappy that it won’t be able to exercise a veto on the arrangements, after Johnson diluted it in an effort to secure the EU’s backing for his plans.The DUP’s view matters because the opposition of the party’s 10 MPs contributed to Johnson losing a key Brexit vote on Saturday. Can he win them over? Unlikely, as my colleague Dara Doyle has explained here.Johnson Has a Big Brexit Problem: His Northern Irish FriendsScotlandIf they can have it, why can’t we? Voters in Scotland, who overwhelmingly wanted to remain in the EU, are unlikely to relish the idea that Johnson’s deal will give Northern Ireland special treatment. The province will be closely aligned with the EU’s customs rules, potentially giving companies in the region an advantage over their Scottish peers.The Scottish National Party will almost certainly ramp up pressure for a second independence referendum after Brexit. Will Johnson be able to avoid the breakup of the U.K.?2020 Cliff EdgeThe Withdrawal Agreement Bill creates a new cliff edge: If a free trade agreement hasn’t been reached with the EU by the end of 2020 (or up to two years later, if both sides agree) then we are back to leaving without a deal. When Conservative MP John Baron pointed that risk out in a BBC interview, waverers took it to mean that Johnson isn’t serious about leaving with a divorce agreement.The Not-So-Level Playing FieldThe prime minister moved the U.K.’s commitments to abide by EU standards on tax, labor protections and environmental standards from the Withdrawal Agreement into the Political Declaration — which, crucially, isn’t legally binding.Johnson has pledged to protect labor rights, but opposition Labour politicians are deeply skeptical he really means it. He will need to convince at least a few to believe him if he is to get his deal through Parliament.Second Referendum?Labour is backing an amendment to put Johnson’s Brexit deal to hold another referendum — something the government has so far resisted.(Updates cliff edge section.)To contact the reporter on this story: Edward Evans in London at email@example.comTo contact the editors responsible for this story: Tim Ross at firstname.lastname@example.org, Stuart BiggsFor more articles like this, please visit us at bloomberg.com©2019 Bloomberg L.P.