However, a small percentage of households will benefit from itemizing their deductions instead of using the standard deduction. The tax code is littered with special deductions. Some, like the home mortgage interest deduction and the deduction for state and local taxes, are huge. In 2013, the Congressional Budget Office (CBO) estimated that those two deductions will each reduce government revenues by more than $1 trillion from 2014-2023. The vast majority of these benefits accrue to high-income households.

If a policymaker is serious about simplifying the tax code, consolidating tax brackets is not enough. They also have to clean out all of these tax breaks—and that’s exactly what Lee and Rubio want to do. They would eliminate just about every tax deduction, with the exception of the deduction for charitable giving and a reformed mortgage interest deduction (although they don’t say how it’s reformed). In return for eliminating the standard deduction, they would create a new $2,000 personal tax credit ($4,000 for joint filers).

But the most important change would be a huge expansion of the Child Tax Credit. Currently, families can collect a credit worth up to $1,000 per child, although the exact amounts can vary. The Rubio-Lee plan would raise that to $2,500 per child and make it refundable against payroll taxes, both on the employer and employee side. But it's not fully refundable, causing it to leave out many poor and non-traditional families. A better idea, as The New Republic's Elizabeth Stoker Bruenig has proposed, would be a child allowance available equally to all parents.

At the end of their 26-page proposal, Rubio and Lee give examples of how their plan would affect various American households. A joint filer with $50,000 in income, two children, $1,500 in charitable income, $1,000 in student loan interest, and $2,500 in retirement savings would save $4,500 a year, for instance. But as when any politician releases a tax plan, these are examples of American households who would benefit most—in this case, families with kids. Beyond that, the senators don’t give any details on how their plan affects the progressivity of the tax code.

When former Representative Dave Camp released a tax plan almost a year ago, he learned how hard it was to overhaul the tax code. His plan consolidated tax brackets, lowered rates and cleaned out the tax code, in ways similar to Rubio-Lee's. But it also imposed a new tax on too-big-to-fail banks and taxed capital gains as ordinary income—a non-starter for many Republicans. Mitch McConnell, then the Senate Minority Leader, said the plan had “no hope” of passing. For those hoping for a major overhaul of the tax code, the reaction on the right to such a credible, conservative pan was disappointing.

Lee and Rubio are hoping to avoid that fate—and may have found a way to do so. The reason Camp had to impose a tax on banks and tax capital gains as ordinary income is that it’s basically impossible to accomplish all conservative tax goals while keeping the plan revenue-neutral. Lee ran into this same problem with the first draft of his tax plan, which the Tax Policy Center scored as increasing the deficit by $2.4 trillion over the next decade. So when it came to this new proposal, Lee and Rubio decided they wouldn’t make it deficit neutral. It’s far easier to make a tax plan that appeals to all Americans when you raise less revenue than the current tax code.

In some sense, this isn’t a huge problem. As Rubio and Lee write, their plan is a first step on the long road to comprehensive tax reform. “A potential drawback to the Lee-Rubio plan — which will surely draw headlines as Rubio gears up to run for president — is that it swells the deficit,” Ramesh Ponnuru, who calls the proposal the “most pro-growth tax reform since Calvin Coolidge's presidency,” wrote at Bloomberg View. As Ponnuru writes, a major tax cut doesn’t necessarily have to blow a hole in the budget; it just has to be accompanied by huge spending cuts.

For those on the left, that’s a dealbreaker. Given the rising cost of Medicare, Medicaid, and Social Security, we’re going to need more revenue in the future, not less. Of course, few people on the left or right will say that. Even Democratic plans are generally revenue-neutral. But unless the health care cost curve bends considerably, we’ll hit a point in the near future where we will no longer be able to avoid this obvious problem.

Some on the right understand this as well. The American Enterprise Institute's James Pethokoukis, who largely supports the Rubio-Lee plan, posed a question to former Florida Governor Jeb Bush in Politico recently. “Given the aging of American society,” he wrote, “do you think the U.S. will need to tax and spend more (as a share of GDP) over the next 25 years than it did in the past 25 years?” Reihan Salam, the executive editor of National Review and also a Rubio-Lee fan, applauded Pethokoukis’s question and followed it up on Twitter:

In a nutshell: US is getting older. Will we have to tax and spend more to bear the Boomer burden or do you have a super-magical plan? — Reihan Salam (@reihan) February 27, 2015

Rubio and Lee apparently have a “super-magical plan.”

My biggest concern with Rubio and Lee’s plan is that it will cause Republicans to drop their commitment to revenue-neutral tax reform. They will see a comprehensive proposal that checks off nearly every conservative box and decide that a major tax cut is the way to go. If that happens—if the Overton window moves in a conservative direction—it will blow up the small chance that comprehensive tax reform could happen anytime soon.

This post has been updated to better reflect the effect of the CTC expansion.