The Senate is scheduled to start a procedure around 2:15 p.m. (Eastern time) today that could drastically change health care law in this country — but nobody, including Senators, seems to know exactly what the vote is on. In the last remaining hours before the votes are cast, here’s what we do know.

What’s Going On

Senate Majority Leader Mitch McConnell (KY) has put forth proposals to repeal and/or replace the Affordable Care Act (Obamacare) as a budget resolution.

In order to make that happen, he has to get a simple majority of 51 Senators to vote in favor of a motion to proceed. Mathematically speaking, there are 52 Republican members of the Senate, but not all are expected to be in favor of the motion to proceed. So McConnell needs at least 50 to vote yes, with Vice President Mike Pence in his back pocket as a tie-breaking 51st vote if needed.

But as we explained yesterday, the text put in front of the voting Senators on which they can vote (or not) to proceed doesn’t actually have to be the text of the proposed bill. It can be a placeholder — and because no actual bill has yet gained the approval of 50 or more Senators outright, it has to be.

McConnell has been proposing various strategies and compromises in order to get more moderate Republicans and hardline conservatives on the same page and both willing to vote for the motion to proceed. The strategy that seems to be sticking, sources tell Vox, is a “skinny repeal,” in which the Senate votes on a proposal that rolls back many, but not all, provisions of the ACA.

What “Skinny Repeal” Entails

The “skinny repeal” is basically what it sounds like: a narrowly-targeted repeal bill that reverses some provisions of the ACA.

According to Vox, the bill proposes to functionally eliminate the individual mandate — the part of the law that requires people to get coverage — by eliminating the penalty for not getting coverage. The skinny repeal also rolls back the employer mandate (the thing that says workplaces of a certain size and type have to offer coverage) and several taxes that pay for it all.

However, removing the individual and employer mandates effectively tanks the law.

The Congressional Budget Office determined earlier this year that a repeal of the individual mandate would cause an estimated 18 million currently-covered Americans to lose their insurance within a year.

The CBO also found that the marketplaces would enter a precipitous decline, as people withdrew from the exchanges, and that would in turn raise premiums and costs as only those with the highest care needs would stay in plans.

That, then, would render plans unaffordable to lower-income patients who needed to buy them, and would keep increasing the uninsured rate — which would make insurers pull out of the marketplace, deeming the number of customers no longer worth the cost.

In total, the CBO estimated, the individual mandate repeal would leave a total of 59 million Americans without coverage by 2026.

Another recent analysis found that repealing the ACA would cause more than a million Americans to lose their jobs.

Health care is a huge employer — nearly 16 million Americans have jobs in the industry, roughly 1 in 9 workers nationwide. But if fewer people have insurance, fewer people seek care — which means folks who work at hospitals, nursing homes, and other medical-related facilities get the pink slip.

Now What?

The Senate’s plans so far have been deeply, overwhelmingly unpopular. Basically everyone who isn’t in the Senate has come out against the current bills, including hospital groups, doctor groups, all the major health care issue groups (i.e. American Cancer Society), and in fact the actual insurers themselves.

Meanwhile, in the Senate it’s been a rough road and a mixed bag. As recently as last week, Sens. Susan Collins (ME) and Rand Paul (KY) were firmly against the BCRA, for different reasons, and were eventually joined by Sens. Mike Lee (UT) and Jerry Moran (KS).

When McConnell then suggested voting on a straight repeal, he drew opposition once again from Collins, this time joined by Sens. Shelley Moore Capito (WV) and Lisa Murkowski (AK).

However, the only Senator to remain a firm, known “no” is Collins; all of the others are considered up in the air and could vote either way, depending on what it actually is that McConnell, in the end, proposes.

Stay tuned. We’ll all find out what the Senate actually votes on — and how they vote on it — later this afternoon.

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