Congressional Republicans face critical decisions this week as they move within striking distance on a major legislative package to cut taxes, an achievement party leaders say is crucial to stabilizing the party’s recent political tailspin ahead of next year’s elections.

The House plans to vote on a Republican tax bill by week’s end that would slash taxes for companies and overhaul the tax code for virtually every American family and individual. And the Senate Finance Committee plans to vote on its version of the package within the next few days.

Stark differences between the House and Senate tax bills remain unresolved, but there is enough overlap and – so far – muted intra-party resistance, making the White House increasingly optimistic that an agreement can come by Christmas, as President Trump has repeatedly promised.

Still, potential quagmires remain. House and Senate Republicans risk colliding over whether Americans should be able to deduct local property taxes from their federal taxable income.

The House Republican bill would allow Americans to deduct up to $10,000 of those taxes from income as a way to placate conservatives in high-tax states such as New York, New Jersey and California.

Senate Republicans in their proposal have so far refused to allow for the deduction of any property taxes.

Meanwhile, House and Senate bills differ importantly on how a huge corporate tax cut would go into effect. In the House Republican bill, the tax rate for corporations would fall from 35 percent to 20 percent in 2018. In the Senate bill, the tax cut wouldn’t take effect until 2019, delaying some benefits for corporations but shaving more than $100 billion off the cost of the change.

Congressional Republicans have not indicated how they plan to address this discrepancy, but finding agreement on the timing of the cuts and how to treat property tax income would resolve some of the biggest outstanding issues.

Trump and Republican leaders have promised for months that all Americans will receive a tax cut under their plan, but in recent days, party leaders have conceded that these were false statements and that some people’s taxes will actually rise.