Republicans have a math problem.

There’s a long list of taxes they want to cut. But they can’t cut them all, because House Republicans have set a $4.5 trillion limit on the amount of money the federal budget can lose over the next 10 years to tax cuts.

Even such a huge figure is not enough to encompass all of Republicans’ ambitions, which include ending taxes on tips, trimming corporate payments and extending other treasured tax breaks. So members of Congress are negotiating over what they can actually squeeze into their bill — and what they’ll have to leave out.

In today’s newsletter, I’ll walk through the Republican wish list. I’ll also explain how Senate Republicans want to use what is essentially a budgetary cheat code to make the math problem much easier.

The old tax cuts

Much of the $4.5 trillion plan will be eaten up just by keeping the last round of tax cuts in place.

In 2017, during President Trump’s first term, Republicans passed a bill that lowered taxes for individuals and corporations. Then, too, they were trying to cram their ambitions below a ceiling. So they scheduled many of the cuts, including a larger standard deduction and an expanded child tax credit, to expire at the end of 2025. They were betting that Congress would not let taxes go up on many Americans.

They were right. But keeping taxes where they are now will cost roughly $4 trillion over 10 years. And a few business tax breaks are already phasing out. Restoring those would cost an additional $200 billion. That would leave just $300 billion for other ideas.