London, Britain – Boris Johnson’s Brexit Deal with Brussels at the expense of unionist politicians in Northern Ireland represents a political victory for the United Kingdom’s Prime Minister, but doubts remain over whether he will be able to sell his Parliament.

For many in Johnson’s ruling Conservative party, his plan leaves a bitter taste: breaking promises made to the small Democratic unionist party (DUP), whose support the conservatives relied on to stay in power while potentially boosting their own party’s chances in a likely election.

However, analysts doubt whether Johnson can defy the arithmetic to win MPs’ support for his deal in the historic parliamentary vote on Saturday, pointing to pressure for him to concede a second Brexit referendum that could even halt the UK’s withdrawal from the European Union completely.

European leaders gave Johnson’s deal a cautious endorsement last night yet sent mixed signals about whether it would be the end of the road; leaving open the possibility of extending Brexit beyond the October 31 deadline if MPs reject it.

David Jeffrey, a lecturer in British politics at the University of Liverpool who has studied the Conservative party, said that whatever the outcome, Johnson could make political capital out of recent events.

“Number 10 is doing well at the moment,” Jeffrey said.

“Boris Johnson said he could get the EU to reopen the withdrawal agreement, he could get them back to the negotiating table and get something different, and he’s been ridiculed by critics and he’s done that, so it’s a personal victory.”

Johnson’s Deal

The DUP had led opposition to the so-called “backstop”, an arrangement designed by Johnson’s predecessor former Prime Minister Theresa May to protect the Good Friday Agreement that brought peace to Northern Ireland and under which there must be no physical border on the island of Ireland.

Tim Bale, professor of politics at Ue Mary University London, said the mechanism means Northern Ireland is “essentially both in and out” of the UK and EU customs unions at the same time.

“The irony is that this is very similar to what the EU first came up with a couple of years ago, which Theresa may rejected in favour of her own solution – the Irish backstop,” he said.

Was the DUP sold?

“They got serious concerns about customs controls in the Irish sea and he said he wouldn’t and he’s now effectively signed up to that,” Finnemore said.

Bale of Queen Mary University said that while the majority in Northern Ireland would be relieved about the deal that saves the Good Friday agreement, the DUP would demand betrayal.

“People who talk about Johnson throwing the DUP under the bus or selling them have a point,” he said.

“He made promises about not agreeing to anything that would mean a border flowing through the Irish sea, which he clearly broke.”

The prime Minister’s treatment of the DUP will be a key factor for determining the support he can muster for his deal in Saturday’s parliamentary vote, which analysts say will be hard to win.

He has lost DUP’s support, the opposition Labour Party has rejected his plan as “worse than May’s,” and rebel Conservative MPs opposed to his plans might be unwilling to back him.

Two key groups now hold the fate of his deal in their hands – a hardline Conservative Brexit caucus in the so-called European Research Group (ERG), and a handful of Labour MPs who may be willing to support a deal to end the deadlock.

Phinnemore said: “the ERG are making noises that they are willing to support this deal and there have always been questions about how much they were really going to take their signal from the DUP; their real commitment is Brexit.”

Geoffrey said that while there was a “two-thirds chance” that Johnson would not get his case through, much depended on how he worked labour MPs.

“He has a day-and-a-half to convince them,” Back it up, it’s the only game in town.”

The strategy of “no transaction”?

The theory that puts the spotlight on Johnson’s Brexit adviser Dominic Cummings suggests that the Prime Minister expects to lose Saturday’s vote as a way to secure a” no deal ” Brexit favoured by hardliners.

Geoffrey said: “What the DUP may be gambling on, or what Johnson may have up his sleeve to say is’ I brought a deal but Parliament rejected it, so now we’re acting without a deal ‘ and he got the moral authority to do it because he was trying an alternative.”

But Finnemore believes that despite tough language insisting he will not push through a deal if necessary- “do or die” – Johnson’s position has changed and he essentially wants an agreement with the EU.

“He has abandoned this rhetoric of late and the fact that he has moved significantly in the Northern Ireland dimension to secure a deal reflects the fact that he honestly does not think a deal would not be in the UK’s interest,” he said.

How likely is a referendum?

All eyes will now be on how the parliamentary numbers stack up, and whether supporters can stay in the EU after a second referendum, the focus of a major March to Parliament scheduled for Saturday.

MPs opposed to Brexit were said to be pulling back from plans to force a vote on a referendum amid fears they do not have enough backing.

Bale said the referendum would be the only thing preventing Johnson from using most of the potential results of Saturday’s key vote in the upcoming election.

“It’s hard not to see it as something of a win-win for Johnson,” bale said.

“The only fly in the ointment would be if MPs managed to attach the holding of a referendum as a condition of backing the deal – which would be very uncomfortable for him.”