Mitch McConnell has just turned the immigration debate in the Senate, already mysterious and complicated, into something everyone in Washington is struggling to wrap their heads around.

He’s giving the Senate a week of floor debate to address any immigration issue that members wish: addressing the fate of the 690,000 unauthorized immigrants facing the loss of their protections from deportation and work permits under the Deferred Action for Childhood Arrivals (DACA) program, as well as the fate of the other “DREAMers” who came to the US as children and didn’t or couldn’t apply for DACA; Trump’s border “wall”; policy toward asylum seekers and unaccompanied children at the border; the future of legal immigration to the US; and anything else that senators think is particularly important.

Instead of focusing the debate by introducing a bill and using amendments to push it to the right or left, McConnell is starting the debate with nothing. One of two things will happen from there: Either he’ll have each side introduce amendments to build an immigration bill from scratch or he’ll reveal an amendment of his own that represents a compromise as Mitch McConnell defines it.

That raises the question of what represents a compromise on immigration to Mitch McConnell. He’s not tipping his hand in the slightest. And in the meantime, he’s essentially saying, “Immigration: talk amongst yourselves.”

McConnell is starting the debate a week before the Senate’s February recess — meaning that he’s either asking senators to solve America’s most contentious policy issue in five days or telling them to pause in the middle of a floor debate, spend a week being yelled at by constituents, and come back to take some very difficult votes.

The Senate can’t agree on a starting point, so McConnell is opening the debate up even wider

Because immigration is such a broad and complicated issue, and it’s not clear what McConnell’s priorities are in narrowing it, it’s hard to predict what amendments will be offered. But various divides have already erupted among senators — and it’s not clear whether, in any of these debates, one side or the other has the 60 votes necessary to pass.

Who is getting legalized and how? Legalization proposals from Democrats and immigration-dove Republicans, as well as the White House’s one-page immigration framework, have proposed allowing both DACA recipients and other DREAMers to apply for legal status and eventually become eligible for citizenship. Proposals from immigration hawks in Congress, meanwhile, have offered legalization only to current DACA recipients, and haven’t included any way for them to apply for citizenship after getting legalized. It’s not clear whether there’s a 60-vote consensus for how many immigrants a legalization deal should cover, or for whether they should get a path to citizenship. And while Sen. Jeff Flake (R-AZ) plans to offer a proposal to simply extend the temporary protections DACA recipients currently have for another three years (something that sounds easier in theory than it would be in practice), it’s not clear that there are 60 votes for that either.

Legalization proposals from Democrats and immigration-dove Republicans, as well as the White House’s one-page immigration framework, have proposed allowing both DACA recipients and other DREAMers to apply for legal status and eventually become eligible for citizenship. Proposals from immigration hawks in Congress, meanwhile, have offered legalization only to current DACA recipients, and haven’t included any way for them to apply for citizenship after getting legalized. It’s not clear whether there’s a 60-vote consensus for how many immigrants a legalization deal should cover, or for whether they should get a path to citizenship. And while Sen. Jeff Flake (R-AZ) plans to offer a proposal to simply extend the temporary protections DACA recipients currently have for another three years (something that sounds easier in theory than it would be in practice), it’s not clear that there are 60 votes for that either. What about the parents of DREAMers? Immigration hawks are particularly concerned that allowing DREAMers to become citizens will allow them to sponsor their parents for citizenship. The Senate will have to decide if parents of DREAMers should be specifically barred from becoming citizens through their children. If so, the Senate will have to decide whether to offer some form of temporary legal status to parents instead (as the compromise bill proposed by Sens. Graham and Dick Durbin (D-IL) proposed) or simply keep them in the shadows.

Immigration hawks are particularly concerned that allowing DREAMers to become citizens will allow them to sponsor their parents for citizenship. The Senate will have to decide if parents of DREAMers should be specifically barred from becoming citizens through their children. If so, the Senate will have to decide whether to offer some form of temporary legal status to parents instead (as the compromise bill proposed by Sens. Graham and Dick Durbin (D-IL) proposed) or simply keep them in the shadows. How much money does the wall get? The White House wants $25 billion. The Graham-Durbin bill offered $1.6 billion. Another bill offered by Sens. John McCain (R-AZ) and Chris Coons (D-DE) offers $0, instead proposing a study of border needs. Is there a number between $0 and $25 billion that 60 senators can agree is worth spending on a wall? Maybe! But we have no idea what that is yet.

The White House wants $25 billion. The Graham-Durbin bill offered $1.6 billion. Another bill offered by Sens. John McCain (R-AZ) and Chris Coons (D-DE) offers $0, instead proposing a study of border needs. Is there a number between $0 and $25 billion that 60 senators can agree is worth spending on a wall? Maybe! But we have no idea what that is yet. Can closing “loopholes” stop gang members from entering the US without hurting children fleeing persecution? Trump’s Department of Homeland Security — and, increasingly, Trump himself — is less concerned about money for the border than with changing the law to make it easier to turn away unaccompanied children from Guatemala, Honduras, and El Salvador, and easier to deport them after they have been allowed to enter the US. The White House considers this an important tool to fight the revival of MS-13 activity on the East Coast. Democrats consider it a recipe for disaster that will result in would-be refugees being sent back to their deaths.

Trump’s Department of Homeland Security — and, increasingly, Trump himself — is less concerned about money for the border than with changing the law to make it easier to turn away unaccompanied children from Guatemala, Honduras, and El Salvador, and easier to deport them after they have been allowed to enter the US. The White House considers this an important tool to fight the revival of MS-13 activity on the East Coast. Democrats consider it a recipe for disaster that will result in would-be refugees being sent back to their deaths. Does the Senate care about abolishing the “visa lottery” ? A nd if it does, what does it want instead? Eliminating the diversity visa, or at least eliminating the lottery used to select who gets to apply for a visa, has become a priority for Republicans because it’s a priority for Trump. It’s not clear whether it’s a priority for 60 senators. Even if it is, they might not agree on whether to cut the 45,000 slots currently allocated to the diversity visa or just reallocate them. Even if they agree to reallocate them, they might not agree on whether to make sure they keep going to people from countries that don’t send many immigrants to the US.

Eliminating the diversity visa, or at least eliminating the lottery used to select who gets to apply for a visa, has become a priority for Republicans because it’s a priority for Trump. It’s not clear whether it’s a priority for 60 senators. Even if it is, they might not agree on whether to cut the 45,000 slots currently allocated to the diversity visa or just reallocate them. Even if they agree to reallocate them, they might not agree on whether to make sure they keep going to people from countries that don’t send many immigrants to the US. Should legal immigration be cut, shifted, or neither? The only Senate immigration bill the White House has actually endorsed isn’t about any of these issues. It’s the RAISE Act, sponsored by Sens. Tom Cotton (R-AR) and David Perdue (R-GA), which would slash legal immigration to the US by as much as 50 percent over the next decade by making huge cuts to family-based immigration without expanding employment-based immigration to match it. Nothing is stopping Cotton from introducing the RAISE Act as an amendment next week — except the prospect of getting 60 votes for it. Instead, immigration hawks might decide to propose more modest cuts to family-based immigration. Or they might decide to propose keeping overall immigration levels similar but shifting some slots away from family-based immigrants so that more employment-based immigrants can come into the US instead.

The only Senate immigration bill the White House has actually endorsed isn’t about any of these issues. It’s the RAISE Act, sponsored by Sens. Tom Cotton (R-AR) and David Perdue (R-GA), which would slash legal immigration to the US by as much as 50 percent over the next decade by making huge cuts to family-based immigration without expanding employment-based immigration to match it. Nothing is stopping Cotton from introducing the RAISE Act as an amendment next week — except the prospect of getting 60 votes for it. Instead, immigration hawks might decide to propose more modest cuts to family-based immigration. Or they might decide to propose keeping overall immigration levels similar but shifting some slots away from family-based immigrants so that more employment-based immigrants can come into the US instead. What about interior enforcement? The White House’s attention toward cutting legal immigration has kind of crowded out immigration hawks’ requests for a crackdown on immigration in the interior of the US — including everything from defunding “sanctuary cities” to expanding mandatory use of the E-Verify system to check the legal status of employees. But some immigration hawks, including Sen. Chuck Grassley (R-IA), the head of the Judiciary Committee, are still concerned about the interior. And they might be concerned enough to wedge it into the floor debate.

It’s possible that several of these issues will get rolled into a single amendment in the hopes that that amendment can get 60 votes. But then whichever party is willing to propose such an amendment has to hope that 20 of those senators don’t vote for any other amendment the other 40 senators consider a poison pill.

There are more than enough proposals — but McConnell wants to start from scratch

Various groups of legislators have already introduced bills that include some form of legal status for DACA recipients (or DREAMers more broadly) alongside whatever immigration enforcement provisions or cuts to future legal immigration they think are appropriate trade-offs.

The authors of each of those bills hoped that their bill would be selected as the starting point for the floor debate. But there wasn’t anywhere near a consensus on which bill to pick — or even what issues the bill should address (whether it should include cuts to future legal immigration and/or increased immigration enforcement in the interior; the extent of money it gave for border security; and how many DREAMers it would legalize, and how).

McConnell’s solution to this problem is to choose none of those bills as a starting point.

This actually gives the Senate an even wider menu of options than they already had. Almost all the bills that have been introduced were intended to be, to some extent, compromises — and they were almost all intended to address multiple issues at once.

And this whole floor debate could be a sideshow while real negotiations are happening in private.

Several groups of legislators are theoretically working on new immigration compromises, and none of them have figured one out yet — probably because the biggest splits among legislators aren’t even on policy, but on the question of how important it actually is to pass a bill in the coming weeks. But if they do make a breakthrough, or if McConnell works something out himself, that compromise would be introduced as the new starting point.

But envisioning a compromise bill requires knowing which immigration proposals can get 60 votes in the Senate, which is exactly the problem.

It would be very easy for the open debate next week to result in a bill whose ultimate support is less than the sum of its parts. It could be just as easy for every amendment to fail. The Senate has to thread a very narrow needle — in very little time.