LONDON — It’s up to the politicians now.

In Brussels, the negotiators think they have taken things as far as they can. It’s now for Theresa May to deal with the politics back home, they say.

After a chaotic weekend of intense Brexit talks and an ultimately fruitless last-minute dash to Brussels by Brexit Secretary Dominic Raab, the government says a deal is still close. May told MPs Monday that the two sides are not "far apart."

But the government insists there are issues of real substance still outstanding. What are they? Here's POLITICO’s guide:

Where have we got with the backstop?

Not very far.

Right now, as the U.K. prime minister made clear in the House of Commons Monday, the EU has not moved an inch on the main sticking point in the negotiations.

Michel Barnier is still demanding an insurance clause written into the final divorce agreement that applies to Northern Ireland — and only Northern Ireland — to prevent the need for a hard border between north and south in Ireland.

This “backstop,” as currently designed, would ensure Northern Ireland stays in the EU’s customs territory and sticks to Brussels regulations “unless and until” a new U.K.-EU free-trade deal comes into force guaranteeing the border stays open.

What is this backstop to the backstop?

Ignore it, it's not a thing.

Well, Theresa May used the phrase in her statement to MPs but the EU has not changed its position — it still wants the same backstop it has always wanted. The U.K. is trying to negotiate something else entirely to sit alongside the backstop in a bid to ensure it never actually comes into force. No. 10 is now calling this "the backstop," but it is nothing of the sort.

What’s the problem with the EU's backstop again?

May has said such a clause is unacceptable because it would create a customs border between Northern Ireland and the rest of the U.K. if it ever came into force — something the prime minister, again in a statement to parliament Monday, made a point of saying MPs had already voted to make illegal.

Is customs the only problem?

No. The Democratic Unionist Party says forcing Northern Ireland to accept Brussels regulations is only acceptable if mainland Britain does as well — effectively keeping the U.K. in the single market. May has said that would not honor the result of the referendum because it would mean being a rule taker from Brussels while also having to accept free movement of people.

What solution is the U.K. proposing?

London is prepared to allow some regulatory differences between Britain and Northern Ireland — as long as Northern Ireland agrees (which it doesn’t, as Nigel Dodds, the DUP's leader in Westminster, told May directly in the House of Commons Monday).

Put that problem to one side, the crux of London’s offer is for the whole of the U.K. to remain in a “temporary customs arrangement” with the EU until whatever future trade deal can be agreed to take its place. If agreed, this “bridge” would mean the backstop never comes into force because there would never be a need for it.

What's the problem?

May told MPs that the EU is willing to "explore" the idea of a temporary customs arrangement, but that it is a matter to be discussed along with the rest of the future relationship issues, meaning after Britain's leaving date in March 2019.

Ultimately, the EU says there's not enough time left to construct a special all-U.K. customs bridge before Britain leaves the EU on March 29, 2019, May told MPs.

Is the EU okay with Britain staying in a customs union in principle?

Yes. The EU says the U.K. can stay in the customs union beyond the proposed transition period, which lasts until December 31, 2020 — as long as it signs up to the backstop first. In other words, sign the divorce papers and then we'll talk.

But May has said the backstop is unacceptable?

Yes.

Can she sign it anyway if the EU promises it will never be used?

Maybe. This might well be the test she has to pass.

The U.K. government is under enormous pressure from MPs to ensure the customs “bridge” it is constructing to avoid the backstop is only “temporary” — lasting no later than the end of 2021.

There’s an obvious problem here. As one senior U.K. official familiar with the state of the negotiations said: "If you time-limit the bridge, and at that point haven't reached an end-state customs relationship that the U.K. and EU are both comfortable with, then the EU will want the backstop to kick-in."

So what is the U.K. proposing?

To time-limit the EU's backstop.

What’s wrong with that?

Dublin — and Brussels — say you can’t have a time-limit on an insurance policy. It would be like buying life insurance that no longer applies once you’ve passed 50.

Are there any other problems?

Yes, the U.K. still has a problem with a backstop being Northern Ireland-specific — even if it never comes into force.

Why?

Because once the U.K. has agreed to keep Northern Ireland in the customs union and parts of the single market in all circumstances, then to stop a border developing in the Irish Sea the whole of the U.K. has to do the same and this is unacceptable to the Conservative Party.

So, what future relationship does the U.K. eventually want with the EU?

The plan that May's Cabinet (minus some ministerial resignations) agreed at her Chequers country residence back in July. This is basically a souped-up free-trade deal — under which the U.K. would accept EU rules for goods, agriculture and food after Brexit — and a special new “facilitated customs arrangement” that will see London acting as the EU’s customs agent at its own borders. May claims this will mean the U.K. can avoid any customs checks and lower tariffs with other countries to strike independent free-trade deals.

What does the EU say?

The EU has ruled out Chequers and twice rejected the facilitated customs arrangement as unworkable.

So where are we?

Stuck. According to negotiators, everything else has been agreed at a technical level.

So it’s up to the politicians — still.