For supporters of the public option, this week is a crucial one. Congressional Democrats and the White House are finalizing the specifics of a delicate health care compromise that they hope to move forward next week. The procedural and political challenges facing supporters of reform in Washington are complex and changing rapidly. Will a government-run plan make the cut? Here's an abridged explanation of what's going on in the nation's capitol.

The most important piece of news that trickled out yesterday comes from the Senate parliamentarian, who has reportedly told Senate Republicans that the House must pass the Senate health care bill (and President Obama must sign it) before any fixes can be made to the measure through the budget reconciliation process.

If the House leadership can find some solution to the abortion question (or secure enough pro-choice, Blue Dog votes) and pass the Senate bill as is, then both chambers would collaborate on a set of amendments they could pass through reconciliation (known colloquially as a "sidecar"), satisfying the legitimate concerns of progressive House Democrats about the Senate version. That package would increase the amount of subsidies available for working-class people, raise the threshold on the excise tax for high-cost insurance plans, and boost Medicaid assistance to all states, not just Nebraska. It would also only need 51 votes to pass. What's unclear is whether lawmakers would include a public option in this bundle of fixes. While popular among voters and gaining support in the upper chamber, it would not be a lock to pass. And failing to pass a sidecar would poison the already-strained relationship between the Senate and House Speaker Nancy Pelosi. Not too mention, the bill would be less progressive.

Moving a bill through reconciliation also requires that all portions satisfy the Byrd rule, which says any measure passed through reconciliation must be directly related to the federal budget. Republicans have already promised they will challenge every word in the reconciliation sidecar to see if it qualifies. So the Democratic leadership, including Majority Whip Dick Durbin, must take extra precautions to ensure their bill satisfies all of those requirements. If it doesn't, the sidecar would have to be passed as a regular bill, which the GOP would filibuster, requiring 60 votes to pass cloture. The Democrats definitely don't have 60 votes to approve the changes the House wants, putting the party in the same position as above.

If it is not written into the sidecar, Sen. Bernie Sanders has agreed to introduce an amendment adding a public option. That provision would probably stand up to a Byrd Rule challenge. It might very well pass, too. What Sen. Durbin and others in leadership are worried about, however, is that allowing members to vote on one amendment would open the floodgate for the caucus to support other amendments that might be popular but either don't stand up to Byrd Rule scrutiny or would gum up the legislative process. From The Hill:

“We have to urge members to stick with the basic bill,” Durbin told reporters. “And we know Republicans are going to offer a ton of amendments as they always do and we know that if an amendment is adopted, it stops or slows down the process. We have to get this done and move on to more jobs bills.”

Progressive supporters of the public option, including the Progressive Change Campaign Committee, are furious that Durbin would ask members to break promises to their constituents and vote against a public option if it came up in a floor vote. They are even soliciting donations to make a web video targeting Durbin. "We're going to make it radioactive for him to whip against the public option," PCCC founder Adam Green told TPM.

Will pressure from the base, combined with Sanders' assurance that an up-and-down vote is coming no matter what, force the Democratic leadership to work the public option into the reconciliation sidecar? If they do, Durbin is indicating he will whip for it in the Senate. We will see what they decide in a few days.

UPDATE (3:22 pm): At her weekly news conference today, House Speaker Nancy Pelosi (D-CA) made clear that leadership would not include a public option as part of the reconciliation sidecar because she wasn't confident the Senate could pass it. "It's not in reconciliation," she said. "We're talking about something that's not going to be part of the legislation."