The Senate will vote to start their repeal of Obamacare in a few hours - and the process is still in total chaos

On Monday night, Sen. John McCain said he would return to Washington to vote on key issues - most notably, on the Senate's push to repeal and replace the Affordable Care Act.

The dramatic return of McCain, just a week after announcing that he is battling brain cancer, seems to indicate that Tuesday's vote on the Senate healthcare push is extremely close for Republican leaders.

At the same time, though, no one is quite sure of the exact push they're making.

Senate Majority Leader Mitch McConnell said on the Senate floor Monday that there would be a vote on a motion to proceed for the House healthcare bill, the first step in a likely multi-day process of debate and dealmaking in an attempt to come through on the long-held Republican promise of repeal.

The question is whether McConnell's plan is to bring up the repeal and replace bill, known as the Better Care Reconciliation Act (BCRA); the repeal-now-and-replace-later bill, known as the Obamacare Repeal Reconciliation Act (ORRA); or some other modified version of either.

(If you want a full breakdown of the three major pathways and their potential effects, Business Insider's Lydia Ramsey has everything you need to know here.)

It's likely that each of these plans gets brought up at some point, but which one will be pushed by McConnell is anyone's guess - even for Republican senators.

"If we don't know those things when you go in, you're sort of voting in a blind fashion," Sen Rand Paul, a conservative-leaning member of the conference, said on Monday. "I think we need more information. CBO needs to have scored the whole bill."

"I don't have a clue what we're gonna be voting on," said Sen. Ron Johnson, a Republican from Wisconsin. "I just need to know what I'm going to vote on. I'm not real happy with the process."

Despite the confusion, McConnell is set on pushing forward with a vote on Tuesday - at the very least, to get it out of the way.

It appears that McConnell has backing from President Donald Trump. Trump met with a moderate skeptic of the BCRA, Sen. Shelley Moore Capito, in her home state of West Virginia on Monday. On Tuesday, he launched into an early morning tweetstorm urging senators to move forward with the process.

"Big day for HealthCare," Trump tweeted. "After 7 years of talking, we will soon see whether or not Republicans are willing to step up to the plate!"

When the Senate does "step up to the plate" Tuesday, here's a rough outline of how the process will go down:

• McConnell calls for a motion to proceed on the House's American Health Care Act. Since every Democrat is nearly guaranteed to vote no on this motion, no more than two GOP senators can vote against it. Sen. Susan Collins has said she will vote no, leaving McConnell little room for error.
• If the motion succeeds, that begins 20 hours of debate - in legislative time - split equally between Democrats and Republicans.
• The first amendment to be voted on will likely to be the ORRA, to satisfy Paul and other conservatives. This plan is likely to be shot down by moderates.
• The first amendment to be offered procedurally - but second to be voted on, Axios reported - would be the BCRA, which was last updated on July 20. Again, Republicans can only afford two defections.
• According to reports, there is an agreement between more moderate holdout Sen. Rob Portman and conservative Sen. Ted Cruz to add an amendment that would keep the bone structure of the BCRA but add in Cruz's amendment. His amendment would allow insurers to sell non-Obamacare-compliant policies, and the deal would throw in another $100 billion to the state stability fund, a move Portman would support. But that would require 60 votes to pass it has not been scored by the Congressional Budget Office, almost certainly dooming it since there are only 52 Republicans.
• From there, a series of amendments could be added to the House bill, including from Democrats. Additionally, other healthcare legislation could be slotted in for a vote.

In essence: No one knows what the final bill will be, it's unlikely that it will be fully analyzed when it's voted on, and no one known whether it will pass.

Based on reports, the whirlwind session will kick off around 2:30 p.m. ET.