House Ways and Means Committee Democrats are preparing for a series of hearings on the 2017 tax law in the new year after winning the House in the midterm elections.

With Rep. Richard E. Neal (D-Mass.) likely to become the new chairman of the tax-writing committee, Democrats are intent on exploring what is and isn’t working in the new tax code and proposing legislation that would roll back parts of the law (Public Law 115-97) and provide middle-class...