The Republican tax-overhaul effort is in for a marathon debate on the Senate floor at the end of this month, with dozens of doomed Democratic amendments. But the real action will be elsewhere, behind closed doors.

Two parallel and largely private negotiations will determine the content of the bill that’s due for a full Senate vote as early as Nov. 30: One is aimed at getting about a half-dozen wavering GOP senators on board. The other will attempt to smooth the path for a final House-Senate compromise in December.

Neither will be easy. GOP leaders must write a bill that can pass under the Senate’s strict budget rules while cobbling together 50 Senate votes without alienating the House GOP’s coalition of conservatives and moderates from high-tax districts. They’ll also have to avoid political land mines such as the divisive health-care debate that has riven Republicans for much of this year.

Capitol building in Washington, D.C.

House and Senate staff members are already working on ways to avoid a drawn out process for reconciling their different legislation, said Neil Bradley, chief policy officer for the U.S. Chamber of Commerce. He said he’s bullish on the prospects for a compromise next month.

“The fact that they have hit all of their marks so far, it is now more likely,” he said. Key questions include how to tax partnerships and other so-called pass-through entities and how to rewrite international tax laws to limit corporate tax avoidance, he said.

Bill Hoagland, a former GOP Senate staff member who helped shepherd former President George W. Bush’s 2003 tax cuts through Congress, said he’s “totally convinced” lawmakers will try to fast-track the formal methods for resolving House-Senate differences—like a “conference committee” in which members work out differences in a deliberative process.

“A true conference committee would drag out into next year,” said Hoagland, now a senior vice president at Washington’s Bipartisan Policy Center, an independent research group.

Here’s a guide to what to expect:

What’s the schedule from here?

Congress is trying to make a self-imposed deadline of adopting tax legislation by year’s end—to achieve a major legislative accomplishment before the 2018 mid-term elections. But they won’t accomplish much of note this week; both chambers are out for the Thanksgiving holiday. When lawmakers return, the Senate has only 15 legislative days left on its official 2017 calendar. Expect the chamber to vote on a tax bill during the week of Nov. 27.

If all goes smoothly for Senate leaders, that vote would most likely occur late on the evening of Nov. 30 or after midnight on Dec. 1. It’ll come only after a “vote-a-rama,” an overnight series of votes on what could be dozens of amendments offered by both Democrats and Republicans.

While the House approved its tax bill with relatively little drama last week, the Senate vote has much higher stakes. The GOP’s narrow, two-vote majority in the Senate means that if the chamber’s leaders can put together enough votes to pass a bill, the final legislation will probably look a lot like their version.

“The House always has to accede to the Senate because it’s just math,” said conservative economist Stephen Moore. “If you don’t get 50 votes in the Senate, you don’t have a bill. I’ve always thought a lot of the House activity was theatrics and the real activity is going on in the Senate.”

What are the sticking points in the Senate?

Significant differences remain between the House and Senate tax plans: The Senate is proposing to repeal the so-called “individual mandate” that individuals must have health insurance, a requirement of the 2010 Affordable Care Act. Its plan also would delay a corporate income tax cut by one year and would make individual tax cuts temporary; they’d expire in 2026.

Then there’s the issue of state and local tax deductions for individuals: The Senate would repeal them entirely while the House would preserve a property-tax deduction up to $10,000. Even that wasn’t enough to win the support of a dozen GOP House members from high-tax states last week.

Beyond that, the Senate would use a different approach from the House to cutting taxes on partnerships, limited liability companies and other “pass-through” businesses—a potential sticking point among GOP lawmakers. Senator Ron Johnson of Wisconsin last week said he can’t support the plan as written because it offers too many advantages for major corporations and not enough for pass-throughs, which range from mom-and-pop grocers to large, closely held companies to law firms, accounting firms and investment firms.

And a trio of senators has expressed concern about the $1.4 trillion tax cut’s effects on the federal deficit.

How will Obamacare affect the tax debate?

Mustering 50 votes may require some delicate bargaining.

The biggest obstacle may be the planned repeal of the individual mandate imposed by the Obamacare law, a move that would leave 13 million people with no health coverage by 2027, according to the Congressional Budget Office. The change would save the federal government as much as $318 billion by then— because it would have to spend less on insurance subsidies— according to the CBO. GOP tax writers would use that savings to help reduce the deficit impact of the tax cuts.

But Republican senators Susan Collins of Maine and Lisa Murkowski of Alaska have expressed concerns about the move. Neither has drawn a red line on it yet, but Collins said Sunday that the Senate proposal “needs work.”

“I don’t think that provision should be in the bill,” she said of the individual-mandate repeal on ABC’s “This Week” program. “I hope the Senate will follow the lead of the House and strike it.” She said that for some middle-income families health-insurance premiums would increase, canceling out any tax cut the bill would give them.

“That’s the one big potential sticking point— whether they can get 50 votes for repealing the individual mandate in Obamacare,” said Moore, the conservative economist. “If they can’t, then they get stymied again.”

What about fiscal impacts?

The bill’s potential effect on federal deficits and the national debt is already under scrutiny. Three Republicans— Tennessee’s Bob Corker, Arizona’s Jeff Flake and Oklahoma’s James Lankford— have raised alarms about the deficit, which the legislation would increase by $1.4 trillion over a decade, before accounting for the economic growth that its backers say would ensue. Independent analyses suggest there wouldn’t be enough such growth to cover the full cost of the tax cuts.

“The biggest land mine is the tension between addressing concerns of senators that would increase the cost of the bill and senators who are already concerned about the deficit”—as well as some provisions in the bill that some regard as “gimmicks” designed to disguise its deficit impacts, said Ed Lorenzen, a senior adviser for the non-partisan Committee for a Responsible Federal Budget. One such ploy, he said: The bill sets individual tax cuts to expire in 2026— though party leaders say a future Congress won’t let that happen.

Amid the tax debate, Republicans are pursuing a separate deal with Democrats to pursue new federal spending levels. When reports emerged last week that those discussions included talk of a $200 billion spending increase that wouldn’t be offset by other cuts, Corker lashed out.

“We’re $20 trillion in debt, and it’s party like there’s no tomorrow time in Washington,” he said on Twitter. At the same time, Arizona’s John McCain has called for the budget deal to increase military spending, and GOP leaders who want his vote on a budget deal and a tax package can ill-afford to ignore his aims.

So how likely is passage this year?

On taxes, McCain has said he wants the legislative process to follow “regular order.” In the end, that may be the most challenging demand of all— given the time constraints that Republican leaders have set for themselves.

House Speaker Paul Ryan said earlier this month that the House and Senate would work out their differences in a conference committee. “We’re going to conference,” he told reporters at a Nov. 9 news conference. “Why are we going to conference? Because we’re doing this the right way. We’re doing this regular order.”

The speaker’s office is standing by that plan. “We will go to conference,” Ryan spokeswoman AshLee Strong said in an email.

Much will depend on how the rest of November goes. This week, on recess, members of Congress will hear from local constituents on what they like—and don’t like— about the emerging tax legislation. They may be in for an earful.

Last week, Quinnipiac University released a poll that said American voters disapprove of the GOP plan, 52 percent to 25 percent. Overall, voters said the proposals benefit the rich at the expense of the middle class, 59 percent to 33 percent, according to the poll, which had a margin of error of plus or minus 3 percentage points.

The plan is a moving target, of course. But given those numbers— and the other potential obstacles— Stan Collender, a former Democratic congressional aide, said he thinks the prospects for the Senate vote next week “are 50-50.”

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