Under President Trump’s aggressive plan to overhaul the country’s tax code, “retirementsavings will be protected,” according to Gary Cohn, Trump’s chiefeconomic advisor and director of the National Economic Council.

Related: GOP contemplating shift to all-Roth 401(k)system

During a press conference rolling out the framework for theWhite House’s plan for tax reform, Cohn and Treasury SecretarySteve Mnuchin said the Trump plan would eliminate most of the taxbreaks that mainly benefit high-income individuals.

While pledging to protect retirement savings, the White Houseplan does not include details on whether the existing tax-preferredtreatment of contributions to 401(k) and other defined contribution plans arespared under the Trump plan, or whether they will be replaced withnew after-tax incentives to save. Individual deductions on mortgageinterest and charitable giving will be spared.

Related: Existing scoring of lost tax revenue on401(k)s is shortsighted

The Trump plan would lower the corporate tax rate from 35percent to 15 percent, and reduce the existing seven individual taxbrackets to three—10, 25, and 35 percent. A one-page outline of theplan does not include the income thresholds for the new taxbrackets.

The plan would also eliminate the 3.8 percent tax on dividendincome created by the Affordable Care Act, repeal the alternativeminimum tax, and do away with the so-called death tax. The currentstandard deduction would be doubled, meaning the first $24,000 of amarried couples earnings would not be taxed.

“This isn’t going to be easy. Doing big things never is,” saidCohn. “But one thing is certain: I would never, ever bet againstthis President. He will get this done for the American people.”

Cohn and Mnuchin did not say whether the plan would be revenueneutral, but said it would create “trillions” in additional revenuethrough the economic growth the plan would generate and theelimination of most of the existing deductions, such as those forstate and local taxes.

Cohn said the White House is in ongoing “robust” discussionswith leaders in the House and Senate, and that President Trump isdetermined to pass tax reform legislation this year.

The non-partisan Joint Committee on Taxation says definedcontribution plans will cost $583.6 billion in forgone tax revenuebetween 2016 and 2020. Traditional IRAs will cost $85.8.

Republicans are reportedly considering several options thatwould eliminate or reduce the tax-preferred treatment of 401(k)contributions.

Ed Murphy, president of Empower Retirement, recently toldBenefitsPRO that a proposal to shift the entire definedcontribution system to an all after-tax, or Roth structure is“highly unlikely.”

Retirement advocates and non-partisan economists are concernedthat the Roth structure does not provide enough incentive to savefor retirement. A recent report from BrightScope and the InvestmentCompany Institute showed 80 percent of respondents said the pre-taxtreatment of 401(k) contributions are a “big incentive” to save forretirement.

In a statement, House Speaker Paul Ryan, R-WI, and Ways andMeans Committee chairman Kevin Brady, R-TX, said the White Houseplan will “serve as critical guideposts” for Congress.

Some advocates for tax reform are concerned the White House isrelying on overly optimistic growth expectations to rationalize thedeep tax cuts.

“The tax code is in desperate need of reform to simplify it,make it fairer, and grow the economy,” said Maya MacGuineas,president of the Committee for a Responsible Federal Budget, in astatement.

“At the same time, we have to recognize the simple facts thattax cuts are not the same as reforms, nor do tax cuts pay forthemselves. Actual reform is going to require identifying specifictax expenditures to eliminate or reform. Relying on overly rosyeconomic assumptions to offset the revenue loss from tax reductionswill not only lead to disappointing results, it will undermine thepotential growth benefits from reforming the tax code,” addedMacGuineas.

The elimination of some tax breaks under the White House plan isencouraging, MacGuineas said. But “tough choices” will have to madeto assure the aggressive tax cuts can be paid for.