WASHINGTON ― Republican congressional leaders say that reforming the tax code will be an easier lift than their thwarted bid to repeal the Affordable Care Act. But eight months into Donald Trump’s presidency, lawmakers remain at odds over what new tax rates should look like, how they’ll pay for cuts, or whether they even should make up the lost revenue.

With most of Trump’s legislative agenda in limbo, broad consensus exists within the GOP to do something on taxes once Congress returns from recess in September. The key question is how big to go ― whether to push for a major, permanent overhaul of the tax code, which is politically harder to do, or live with a temporary, marginal tax cut that Trump can chalk up as a victory.

Few specifics about the effort have been released so far, but Republicans are already facing an uphill battle.

Trump has proposed slashing the tax rate for all businesses to 15 percent from the current 35 percent. House Republicans, meanwhile, have previously talked about a plan that would reduce the corporate tax rate to 20 percent. (Most companies, meanwhile, pay an effective tax rate much lower than 35 percent.)

There is even less agreement about altering the taxation of small businesses, deductions for corporate interest expenses and the state and local tax deduction. Eliminating such deductions would bring in more revenue to offset the cost of rate cuts, but doing so is considered politically sensitive because they are utilized by millions of Americans.

House Speaker Paul Ryan (R-Wis.) ― who, unlike the president, has been traveling the country this week to drum up support for tax reform ― said Thursday some deductions would indeed have to go. He was careful, however, not to say which ones.

“We recognize, acknowledge and believe you need to maintain the mortgage interest deduction,” he said in an interview on CNBC. “Whether it can be improved and how it works, that’s a discussion we’ll have on an ongoing basis.”

Ryan has said he wants to double the standard deduction that most households use to reduce their taxable income, but he hasn’t said whether reforms would take away personal exemptions that particularly benefit families with children. Even with a bigger standard deduction, taking personal exemptions away could result in a tax hike on middle-class households.

Politico reported earlier this week that options under discussion include a cap on the mortgage interest deduction for homeowners. Negotiators are also reportedly weighing eliminating people’s ability to deduct state and local taxes, which would disproportionately affect liberal-leaning states, as well as “eliminating businesses’ ability to deduct interest, while also phasing in so-called full expensing for small businesses that allows them to immediately deduct investments like new equipment or facilities.”

Groups affected by such proposals ― like the National Association of Realtors, which opposes any reductions to the mortgage interest deduction ― can be expected to lobby hard against such changes.

White House Press Secretary Sarah Huckabee Sanders did not offer any details about a tax reform plan in a press briefing on Thursday, but she told reporters to expect movement in “very short order,” possibly even next week.

Aside from policy, Republicans face several procedural hurdles on tax reform. In order to pass a bill under so-called reconciliation ― rules that would allow Republicans to approve the legislation with a simple majority in the Senate ― the tax cuts must not add to the deficit 10 years after they’re passed. While GOP leaders are optimistic they can craft such a bill, there are already some members, like Rep. Peter King (R-N.Y.), who say that goal is unrealistic.