The big change: The GOP leaders and the White House plan to cut the top tax rate for small businesses — known as "pass-throughs" — from 39.6 percent to 25 percent. (Currently small businesses pay the same tax rates as individuals, and this puts them at a disadvantage to larger corporations, which pay lower rates.)

The so-called "Big Six" tax framework — named because it's been hashed out behind closed doors between six top Republicans and administration officials — will set up a clash with Democrats over the tax breaks that apply to large corporations and upper income Americans.

• Most Democrats have already drawn a red line on tax reform: 45 out of 48 Democratic senators signed a letter saying they wouldn't support any tax bill that adds to the deficit or offers new tax breaks to the wealthiest Americans.
• But Republicans are desperate for a win and appear on course to fund tax cuts with a blend of deficit spending and the closing of loopholes. They will dare Democrats, especially the 10 senators up for re-election in states Trump won, to vote against tax breaks for their constituents.

What's next: President Trump is planning to give a speech unveiling the Big Six framework in Indiana on Wednesday, three sources said. The framework is the starting point for the tax reform process. It reflects the shared view of the Big Six, but it will inevitably change substantially as it goes through the normal legislative processes in the House and Senate.

(The "Big Six" are House Speaker Paul Ryan, Senate Majority Leader Mitch McConnell, Treasury secretary Steven Mnuchin, White House economic adviser Gary Cohn, and the chairmen of the two tax-writing committees — Senate Finance Committee chairman Orrin Hatch and House Ways and Means chairman Kevin Brady.)

The details, per three sources with knowledge of the plan:

• Top individual tax rate cut from 39.6 to 35. The current seven income tax brackets collapsed to three, as part of simplification. (Axios hasn't obtained the other two rates.)
• Axios can confirm that the Big Six agreed to cut the corporate tax rate from 35 percent to 20 percent. That key detail leaked last night to the Washington Post. (Trump has said he wants the corporate rate to be 15 percent.)
• The Big Six framework is also expected to include guardrails to prevent wealthy people from artificially lowering their income taxes by rearranging their affairs to get taxed at the small business rate.
• We can confirm, too, WashPo's reporting that Republicans plan to double the standard deduction — a boost for the middle class and a key component of simplification.

These Big Six decisions have been held incredibly tightly, but details began leaking out around Capitol Hill on Friday night and the corporate rate was first published by the Washington Post's Hill team. By Saturday, influential figures on K Street were beginning to learn more details.

Some problems the Big Six could run into:

• The National Federation of Independent Business (NFIB,) the leading small business association, wants to equalize the small business rate and the corporate rate. Under the current plan, that's not happening. The corporate rate will be 20 percent and the small business rate 25 percent. "That's going to be controversial, but it's not a deal-breaker I don't think," said a source close to the process.
• House conservatives — especially the Freedom Caucus — haven't been involved in the Big Six discussions and they want the corporate rate to be much lower, at 16 percent. Republican leaders say there's no way that's going to happen, and Treasury Secretary Mnuchin agrees.
• The Trump tax plan will likely add to deficits, at least in the short term, which will bother some deficit hawks. But tax reform advocates were heartened when, just this week, Senate Republicans on the Budget Committee cut a deal that would reduce government revenue by as much as $1.5 trillion over 10 years. Republicans argue that, with economic growth spurred by the tax reform, there'll be substantially less lost revenue than $1.5 trillion.
• Realtors and home builders won't be happy with the doubling of the standard deduction. That's because lots more people will take the standard deduction and many fewer will itemize their tax returns. A prevailing belief in the real estate world is that under those conditions, fewer people will take the mortgage interest deduction, which could mean fewer homes being purchased.
• Whichever groups are hit up for the "pay-fors" — the loopholes being closed — will inevitably form lobby groups and oppose those elements of the plan.