After days of optimistic leaks and rumors, British Prime Minister Boris Johnson has done what the European Union said was impossible. He’s successfully re-opened the bad Brexit deal struck by former Prime Minister Theresa May, and won a new deal that is significantly better for Britain.

The light is now flashing green for Brexit.

The problem with May’s deal was that it was designed to trap Britain inside the EU’s regulatory orbit forever. In practice, it meant that Britain would have been locked into a customs union in goods—visible trade—with the EU. 

That would have made it impossible for Britain to negotiate trade deals with other nations. Worse, it would have meant that Britain was, practically speaking, still ruled from Brussels. 

No wonder the House of Commons rejected May’s deal three times, by historic margins.

Johnson’s deal is far better. After a 14-month transition period, Britain will completely leave the EU and the EU’s single market and customs union. There will be a special customs deal for Northern Ireland and its border with Ireland, an EU member.

This is the part of Johnson’s deal that will be controversial. 

The arrangements for Northern Ireland, indeed, are not ideal, as they will be tied to EU customs rules while remaining part of the U.K. customs territory. But the deal does secure an open border between Ireland and Northern Ireland, and gives Northern Ireland the freedom to participate in whatever new trade deals the British government negotiates.

Above all, Johnson’s deal puts Northern Ireland in control of its own destiny. If Northern Irish lawmakers dislike the new arrangements, they will be free to reject them. 

The scene now shifts to the House of Commons, where early indications are that the vote on Johnson’s deal on Saturday will be extremely close. Most Conservative members of Parliament are likely to vote in favor of the deal, but the Democratic Unionist Party, Johnson’s Northern Irish allies, have indicated they will vote no.

The europhile Liberal Democrats will also oppose. That makes the stand of the opposition Labour Party critical. If enough Labour members defect, Johnson’s deal will win. If not, it will lose, and the Brexit uncertainty will continue.

Labour hopes that if it can sink Johnson’s Brexit deal, it can run an election campaign on the theme that Johnson has failed to achieve Brexit. This is a transparent approach. It has nothing to do with the good of the country, and everything to do with party politics.

Johnson is on the verge of a truly historic achievement. He was the victorious leader of the Brexit referendum campaign, and he has now successfully renegotiated Britain’s exit agreement from the EU. 

If he brings Britain out of the EU, he will rank as one of Britain’s great prime ministers.