Spending on social-insurance programs will increase sharply as the U.S. population ages, longevity increases, and expensive new medical therapies continue to emerge. Closing future federal deficits with a wealth tax would require importing a slew of new ultra-millionaires from another dimension and then taxing them with abandon, and that’s before we start contemplating Medicare for all or a Green New Deal, let alone a new federal child-care program.

But imagine for a moment that Warren’s federal child-care program could indeed be paid for, and that fretting over cost control is a hateful exercise. Even then, there would still be reason to tread lightly. In the late 1990s, the Canadian province of Quebec embarked on an eerily familiar experiment. To better the lives of parents and children alike, its government offered heavily subsidized child care at an out-of-pocket price of $5 a day. In short order, Quebec families flocked to the new program, including many who had previously relied on more informal child-care arrangements.

The results were, on one level, a great success. Labor-force participation surged among mothers in the province, which was one of the Quebec policy’s chief objectives. As the economists Michael Baker, Jonathan Gruber, and Kevin Milligan have found, however, the outcomes for the children enrolled in the program were less encouraging. In a 2015 working paper, they reported that the Quebec policy appeared to have had “a lasting negative impact on the non-cognitive skills of exposed children,” one that was particularly pronounced among boys. Needless to say, the findings of Baker et al. are hardly the last word on the subject, and it is certainly possible that a federal child-care program in the United States would yield far superior results, perhaps by drawing on some of the lessons of the Quebec experience. But we can’t dismiss the results of the Quebec policy as the result of negligence or incompetence. Its designers were serious, thoughtful people who wanted to do right by Quebec families, yet their experiment had decidedly mixed results. It would be foolish to discount the possibility that the same might happen south of the border.

Read: When expanding access to child care isn’t enough

Then there is the fact that, as Patrick Brown observes in the latest issue of National Review, a large number of parents would much prefer to care for their children at home than to enroll them in day care. A 2015 Gallup survey found that 56 percent of mothers with children under the age of 18 reported that they would “ideally like to stay home and care for their house and family,” a number that might well be higher for the parents of young children.

Warren’s proposed federal child-care program would do nothing for stay-at-home mothers and fathers. Indeed, the sheer size of the benefit is such that it would nudge many parents who’d otherwise prefer to devote all of their time and energy to raising their children into the workforce. Apart from the fact that this would mean privileging one normative conception of family life over another, a controversial proposition in itself, another danger lurks. By boosting parental labor-force participation, a federal child-care program along these lines could boost household incomes (a good thing), which in turn could drive up home prices in neighborhoods with high-quality schools (a less good thing), thereby setting off a series of “frenzied bidding wars” that compel all two-parent families to become two-earner families, whether they want to or not. Or at least that’s what Warren and her daughter, Amelia Warren Tyagi, argued in their provocative book The Two-Income Trap, published in 2003. At the time, Warren was a professor at Harvard Law School known for her deep interest in the financial fragility of middle-income families and, unusually for academics of her stature, for her heterodox political sensibilities, which blended economic populism with a culturally conservative streak. Judging by her child-care proposal, that Warren has been replaced by someone else entirely.