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The Obamacare repeal debate has begun in the Senate. That’s about all we know for sure.

Senate Majority Leader Mitch McConnell has managed, after prospects looked dim again and again, to open debate on an Obamacare repeal plan. It’s a huge victory for Senate Republicans' hopes of passing some kind of health care bill, and it puts health insurance for millions of Americans at risk. Every plan Republicans are considering is projected to lead to millions fewer Americans having health insurance.

But Republicans haven’t actually settled on what legislation they are trying to pass at the end of this debate. Bills to cleanly repeal much of Obamacare or to more fully repeal and replace the 2010 health care law don’t currently have the votes necessary to pass. In just the past few days, the idea of a much smaller bill, repealing just a few of Obamacare’s most unpopular provisions, surfaced.

That final destination must be sorted out in a mad rush over the next few days, with the Senate’s arcane budget rules and a vote-a-rama, which will open up Republicans to a flood of Democratic amendments designed to force tough votes that could make the process even more treacherous.

Senate Republicans scored a victory Tuesday. But the ultimate result is far from clear. Let’s break down how the next few days will look.

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This is what will actually happen in the Senate over the next day or so

The Senate’s process from here is byzantine. The vote on Tuesday was technically to start debate on the House’s health care bill, but nobody expects that to be the actual legislation the Senate ultimately votes on.

This is what we expect to happen now, per Senate aides. Remember, timing and order are fluid. But this is a rough outline.

Two hours of debate on the clean (partial) Obamacare repeal bill.

Two hours of debate on the repeal-and-replace plan that Republicans have been working on since May.

Vote on the repeal-and-replace bill. Because of some last-minute changes to the legislation, it is expected to require 60 votes. That would demand Democratic support, which will never happen, so it looks likely fail.

Vote on clean (partial) repeal bill. It would need 51 votes, but it is expected to fail as well because too many Republicans are opposed to repealing without a replacement.

20 hours of debate on the Senate floor. That is floor time, not real time, so those 20 hours could take a couple of days. Democrats and Republicans will take turns making speeches about health care. Democrats can use certain tactics — like asking for a full bill to be read out loud — to make the process more painful.

Vote-a-rama. This is a lengthy series of amendments offered by Republicans and Democrats to amend the bill. Amendments must be considered relevant to health care, and they need 51 votes to be approved. They would technically be amendments to the House bill, if the previous two Senate bills have already failed or not been voted on yet.

Final bill. McConnell will eventually offer a final substitute, encompassing the actual plan that Senate Republicans want to pass. This could be the "skinny repeal" plan that surfaced Tuesday morning.

Vote on passage. That needs 51 votes to pass. Vice President Mike Pence can break a 50-50 tie.More to come. Stay tuned.

Chart of the Day

The many paths before us. This flowchart, from our own Alvin Chang, gives you a sense of how far we have to go — we're only through the "motion to proceed" box at the top — and all the ways things could still go wrong or right for Republicans.

Kliff’s Notes

With research help from Caitlin Davis

Today's top news

“McCain’s return to Senate injects momentum into GOP health-care battle”: “The Senate Republicans’ drive to pass a sweeping rewrite of the nation’s health-care laws took another unexpected turn late Monday when the office of Sen. John McCain (R-Ariz.) announced he would return to Washington for a planned Tuesday vote.” —Sean Sullivan, Kelsey Snell, Ed O’Keefe, and John Wagner, Washington Post

“The Senate Republicans’ drive to pass a sweeping rewrite of the nation’s health-care laws took another unexpected turn late Monday when the office of Sen. John McCain (R-Ariz.) announced he would return to Washington for a planned Tuesday vote.” —Sean Sullivan, Kelsey Snell, Ed O’Keefe, and John Wagner, Washington Post “Senate votes to move forward on Obamacare repeal”: “Republican senators voted Tuesday to more forward on their seven-year pledge to repeal portions of Obamacare, with Vice President Mike Pence issuing the tie-breaking vote to unlock hours of debate to assemble details of a final healthcare bill.” —Kimberly Leonard, Washington Examiner

“Republican senators voted Tuesday to more forward on their seven-year pledge to repeal portions of Obamacare, with Vice President Mike Pence issuing the tie-breaking vote to unlock hours of debate to assemble details of a final healthcare bill.” —Kimberly Leonard, Washington Examiner “A Senate ACA Repeal Vote Isn’t the End of the Fight. It’s Just Round Three”: “There are multiple possible replacements, and if McConnell and his leadership team are able to open debate, members of the Senate may see more than one of them. They range from a measure that would repeal huge swathes [sic] of Obamacare without replacing them to comparatively mild changes to the law that leaves many of the ACA’s requirements and structures in place.” —Rob Garver, Fiscal Times

Analysis and longer reads

“Who Knew Senate Health Bill Debate Could Be So Complicated?”: “The rules for budget reconciliation, the process the Senate is using that limits debate and allows a bill to pass with only a simple majority, comes with a set of very specific rules. Here are some of the big ones that could shape whatever final bill emerges.” —Julie Rovner, Kaiser Health News

“The rules for budget reconciliation, the process the Senate is using that limits debate and allows a bill to pass with only a simple majority, comes with a set of very specific rules. Here are some of the big ones that could shape whatever final bill emerges.” —Julie Rovner, Kaiser Health News “For Trump’s ‘Victims’ of Obamacare, Senate Bill May Be Worse”: “It’s unclear which Senate bill lawmakers will debate Tuesday, but Mr. Trump’s claim is not entirely accurate for either the bill to repeal and replace the current law or the bill that partially repeals it without a replacement.” —Linda Qiu, New York Times

“It’s unclear which Senate bill lawmakers will debate Tuesday, but Mr. Trump’s claim is not entirely accurate for either the bill to repeal and replace the current law or the bill that partially repeals it without a replacement.” —Linda Qiu, New York Times "Price Transparency In Medicine Faces Stiff Opposition — From Hospitals and Doctors": “Jerry Friedman, a retired health policy adviser for the Ohio State University Wexner Medical Center, said the opposition doesn’t stem from genuine concern about patients but from a desire to keep the secret rates that providers have negotiated with insurers under wraps. Transparency would mean explaining to consumers why the hospital charged them $1,000 for a test, he said, adding that providers 'don’t want to expose this house of cards they’ve built between hospital physician industry and the insurance industry.'” —Rachel Bluth, Kaiser Health New

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