President Donald Trump put the pressure on congressional Republicans last week to fall in line or advance an alternative on a tax overhaul by releasing a list of his tax principles.

As lawmakers scramble to respond, they will need to find answers to five big questions dealing with issues such as revenue and deductions that could hold the key to completion of major tax legislation that’s long been the goal of Republicans.

Three plans or one?

The White House tax rollout on Wednesday produced a third contender in the GOP tax sweepstakes, vying with the House Republican tax blueprint and legislation being crafted by Senate Finance Chairman Orrin G. Hatch.

Now, Republicans must develop a framework to blend the three plans into a single tax bill that can be signed into law by the administration’s year-end target deadline. For now, congressional hearings and administration listening sessions loom ahead as proponents pitch the competing plans.

Senate Majority Whip John Cornyn predicted that all three plans — or “three tulips” as he said — would continue to grow on their own while lawmakers and the administration try to forge a common proposal on rate cuts and pay-fors. “Let a thousand flowers bloom,” Cornyn said.

New revenue?

Republicans face the daunting challenge of finding new revenue to help pay for tax cuts.

The House GOP plan centers on a border adjustment tax, or BAT, that would raise $1.2 trillion over 10 years based on ending business write-offs for imports and exempting exports. But the BAT faces strong opposition from GOP senators, retailers and energy companies, and raises its own set of questions including whether it would meet World Trade Organization rules so the United States does not have an unfair trade advantage.

The Tax Foundation said the House GOP plan would require about $191 billion in additional revenue over 10 years so that it does not add to the budget deficit — or in other words, to be revenue neutral based on macroeconomic, or dynamic scoring. 

Treasury Secretary Steve Mnuchin has said repeatedly that Trump’s tax plan would not bust the deficit, but there were few details released Wednesday on how that would happen. Trump’s tax plan released during the campaign, which is similar to what was outlined Wednesday, would need at least $3.9 trillion over 10 years to cover costs, according to the Tax Foundation.

There are few ways for Republicans to raise revenue except through curbing tax breaks or imposing new levies, if rates go down. And potential options already explored by the White House, such as a value-added tax or a carbon tax, lack support on Capitol Hill. 

Fate of deductions?

Vows by the Trump team and by House GOP leaders to streamline the tax code to pay for sweeping rate cuts for individuals and businesses signal the start of a fierce fight over endangered sweeteners.

Crusades against tax breaks have a history of mixed results — and tend to bring out powerful interests on both sides of the debate. 

The Trump and House GOP plans eliminate nearly all tax breaks, but would preserve full write-offs for mortgage interest and charitable gifts. The National Association of Realtors has already raised concerns about the overall Trump plan, saying it would “effectively nullify” the tax benefits of home ownership.

Americans for Prosperity, a conservative advocacy group backed by the billionaire brothers Charles and David Koch, has suggested capping the size of mortgages covered by the interest deduction at $500,000 to raise $325 billion over 10 years. New York GOP Rep. Tom Reed, a Ways and Means member, said the panel is considering whether to allow certain deductions — such as the one for mortgage interest — to be claimed on top of an expanded standard deduction.

There are emerging arguments on both sides for preserving and eliminating popular deductions for payments of state and local taxes and business expenditures on research and development. 

Spending cuts?

The Trump administration has said economic growth would help pay for tax cuts, but the questions about finding revenue and not ballooning the deficit raises a related query. Is it time to consider mandatory spending cuts for potential offsets?

Trump promised during to campaign to protect Medicare and Social Security, which likely puts off the table a less generous cost-of-living adjustment like the chained consumer price index, which could raise $182 billion over 10 years. But a reconciliation bill with instructions for a tax overhaul would be a viable vehicle for other cuts in mandatory spending like the Supplemental Nutrition Assistance Program, which could be on the table.

Office of Management and Budget Director Mick Mulvaney advocated mandatory spending cuts as offsets when he was a member of Congress from South Carolina. But the White House budget chief seemed to make a different argument during a CNN interview last week: What about a tax package without full offsets?

“There’s a difference between a deficit that comes from, say, a wealth transfer payment, a welfare program and a deficit that comes from allowing people to keep more of their more money,” Mulvaney said.

Politics?

Tax legislation is hard no matter the political environment, but there’s widespread agreement that the task is tougher given divisions among Republicans and the challenges facing Trump. That translates to a bonanza for lobbyists and strategists in both parties as they prepare for the 2018 elections.

While a potential tax overhaul has fueled a Wall Street rally, its value as a magnet for voters will hinge on how it fares on Capitol Hill.

Forty-three percent of Americans say they are bothered a lot by the complexity of the tax system, according to a Pew Research Center survey released before this year’s tax-filing deadline. And at least 60 percent of the public say they are bothered a lot that some corporations and some wealthy people don’t pay their fair share in taxes, the Pew poll found.

In light of such such numbers, Democrats are betting the GOP’s tax overhaul will lose traction. And they are sure to pounce if it unravels.

“Voters will give them an F,” Delaware Sen. Chris Coons said.

Despite the risks, Republicans aim for a tax coup and electoral rewards. “It would be a very consequential and impactful change in policy, which is going to be good politics as well,” said South Dakota Sen. John Thune, chairman of the Senate Republican Conference.