WASHINGTON — Since their party swept to power, Republicans have entertained visions of an all-inclusive tax cut — one that could permanently lower rates for individuals, shower corporations with new incentives and deliver President Donald Trump’s sprawling suite of campaign promises.

If only it were so easy.

House Republicans are preparing to adopt a budget plan that puts a $4.5 trillion upper limit on the size of the tax cut. Even such a huge sum is not nearly enough for all of their ideas, so lawmakers must decide which policy commitments are essential and which ones they can live without.

For a sense of the Republican predicament, take a look at the 2017 tax cuts. Many of the measures in that law, including a larger standard deduction and more generous child tax credit, expire at the end of the year. The overriding goal of this year’s bill is to extend the expiring provisions, which provide their largest benefits to the rich, before they end.

But accomplishing just that would cost roughly $4 trillion over the next 10 years. Then there’s a coveted business tax break for research and development — which, in an example of the zigzag of tax policy in Washington, Republicans wound down in 2017 and now want to revive. That would be an additional $150 billion. Allowing companies to once again deduct more of the interest on their debt is $50 billion more.

Those changes are the table stakes. They essentially amount to preserving the status quo. And together they would eat up all but $300 billion of the $4.5 trillion Republicans are giving themselves to cut taxes. That’s not very much money, considering the ambitions Trump and other Republicans have for the bill.

The squeeze is on.

“You do start running out of space to do other things,” said Andrew Lautz, a tax policy expert at the Bipartisan Policy Center, a think tank.

White House press secretary Karoline Leavitt said Trump wants the bill to include his ideas to not tax tips ($100 billion, per the Committee for a Responsible Federal Budget), not tax overtime pay (at least $250 billion), lower taxes for companies that make their products in the U.S. (at least $100 billion) and end taxes on Social Security income (at least $550 billion).

Oh, and don’t forget the state and local tax deduction, known as SALT.

In 2017, Republicans put a $10,000 limit on the amount of state and local tax payments Americans could deduct from their federal tax bill. The cap came over the objections of lawmakers in higher-tax states like New York and New Jersey, and House Republicans from those states have made lifting the $10,000 limit a necessary condition for their votes. They are not shy about threatening to kill the bill in the barely Republican House if left unsatisfied.

Repealing the cap entirely could cost $1 trillion over a decade. More modest proposals to increase the limit would still dramatically add to the cost of the legislation. (Just doubling it to $20,000 for married couples would cost $170 billion). Republicans pushing to lift the cap acknowledge the headache they are helping create for Rep. Jason Smith, R-Mo., the chair of the Ways and Means Committee.

“I know Jason wanted a higher number, so more wiggle room,” said Rep. Andrew Garbarino, R-N.Y. “They all know that SALT has to be part of this equation or it really won’t go anywhere.”

Republicans plan to use a legislative process called reconciliation to pass the bill without support from Democrats. As part of that procedure, each committee is allotted a specific deficit or savings target it has to hit in its section of the legislation.

The Ways and Means Committee is allowed to increase the deficit by no more than $4.5 trillion in its section of the bill, while other committees have been asked to make at least $2 trillion in total spending cuts. Those cuts will largely hit health care and food programs for the poor.

Because the cost of the tax cut needs to net out to $4.5 trillion, Republicans could try raising other taxes, like repealing clean-energy subsidies, so they could accomplish more of Trump’s promises. But privately many Republican tax writers hope they can ignore many of Trump’s ideas.

Lawmakers also are considering extending elements of the expiring tax cuts for only a few more years to contain the recorded cost. In that scenario, Republicans would bet that a future Congress would continue the cuts again, replicating a well-worn strategy that now has them agonizing over tax policy from eight years ago.

Some analysts dislike short-term tax cuts, arguing that investment incentives, for example, best help grow the economy when companies can count on them for the long term. And ideas like raising the SALT cap do little to spur economic growth.

A group of Senate Republicans, including John Thune of South Dakota, the majority leader, wrote Trump a letter Thursday opposing any short-term extensions of the 2017 tax law. They argued that Congress should indefinitely continue the cuts, called the Tax Cuts and Jobs Act.

“Congressional Republicans have an historic opportunity to enact this lasting tax relief,” they wrote. “Failure to act boldly does a disservice to the American people who entrusted us to deliver in November.”