The big question in Washington now is whether rewriting the tax code, which has not been done since 1986, will be any easier than undoing the Affordable Care Act. Republicans are hopeful because they view cutting taxes as central to the party’s identity. Yet the requirement that they not add to the deficit, outlined in the House budget, means they are likely to face more broad and well-financed pockets of resistance.

The plan released on Tuesday as part of the House Budget Committee’s 2018 budget resolution blueprint calls for consolidating tax brackets and cutting rates, repealing the alternative minimum tax and switching the United States from a worldwide tax system to a territorial tax system, which would tax only the domestic income of corporations.

It also calls for a $621.5 billion national defense budget for 2018 and $511 billon for nondefense spending. The most contentious part is at least $203 billion in cuts over a decade in “mandatory” spending on programs such as Medicare and Social Security. And it recommends repealing parts of the 2010 Dodd-Frank Act that ushered in financial regulations after the last recession. If enacted, it would result in a $6.5 trillion reduction in the federal deficit over a decade.

The resolution is of particular importance this year because Republicans must pass it to unlock a procedural tool that would allow them to overhaul the tax code without the support of any Democrats. But it will not be easy to pass.

The fact that the budget blueprint dictates that the rewrite of the tax code cannot add to the deficit could set up a clash between Republicans in Congress and the White House, which has been more open to temporary tax cuts that add to the deficit. Mr. Trump has promised the biggest tax cut in history.