Marco Rubio's paid leave plan won't help working families. But it will really, really help Marco Rubio.

The Values Voter Summit, an annual gathering of conservatives hosted by the anti-gay, anti-abortion Family Research Council, bills itself as an event dedicated to “traditional” values. This usually translates to fire and brimstone about same-sex marriage and reproductive freedom, but, on Friday, Marco Rubio veered off that script and talked about something unexpected from a current Republican presidential candidate: the importance of paid leave.

“One of the greatest threats to family today is that too many Americans have to choose between being there for their children in times of great need, or meeting the basic financial needs of their families,” he said before pointing out that losing a paycheck to stay home with a new baby or sick relative is “simply not a viable financial option for many Americans.”

He’s right. According to the Bureau of Labor Statistics, fewer than 15% of workers in the U.S. have access to any kind of paid family leave, and low-wage workers take the hardest hit when it comes to juggling family and work. According to the same data, just one in 20 workers in the bottom quartile can take time off without losing necessary income.

Rubio’s plan would offer a 25% tax credit to employers who offer a minimum of 4 weeks of paid family leave. The maximum pay out per employee, to full-time and part-time workers, would be $4,000, and the maximum leave time would be 12 weeks. “For instance,” Rubio explained, “if you are offered $1,600 in paid leave for four weeks while you take care of your newborn, which would be the equivalent of about $10 an hour, your employer could claim a tax credit for $400.”

Now here’s another essential part of the plan: it’s fully voluntary. Rubio doesn’t believe the government should require federal leave, and wants to leave it to the market to sort out.

Problem is, the market has already tried, and failed, to sort this out.

“We’ve already let the market have its say,” Terri Boyer, executive director and assistant research professor at Rutgers University’s Center for Women and Work, told me over the weekend.

“I’m concerned about how this will impact the workers who most need it,” she said. “Right now, the U.S. doesn’t require it by law, and neither does this proposal. It’s just an incentive. In the U.S., there are a number of workers who get paid family leave, but they get it through their employers, and they’re usually higher paid professional workers or workers at larger companies. So when I hear something like a tax credit, I think it’s really just going to provide further financial backing to these companies that have the deeper pockets in the first place.”

Plus, there is already a market incentive to offer paid leave: it boosts productivity and helps companies attract and retain workers. That’s exactly why you have companies like Netflix rolling out deceptively lush unlimited leave plans for high-end salaried employees but leaving out the people who work in its DVD distribution centers.

“A number of employers already offer it to their highly valued employees—it’s about employee retention,” Boyer explained. “So if you leave it up to the market, you’ll have a very similar situation to what we have now: paid family leave is offered to certain employees, but not to all.

“And my focus as a researcher has always been that these sorts of work supports reach the low-income people who are working part-time job to part-time job, trying to make ends meet, but aren’t able to do that when they have to take leave,” she continued. “I’m thinking that a tax credit would not provide that kind of access. The types of employers that are there aren’t going to be as incentivized as those larger companies.”

The other problem with Rubio’s plan: it isn’t portable. If you leave your job, something you’re more likely to do if you’re stitching together several part-time gigs, then you leave the benefit behind, too. “And think about the workers who are most at risk here, they do change jobs,” Boyer said.

Ultimately, she summarized the plan this way: “It’s not going to harm anyone, but it’s not really going to help anyone, either.”

But I’d add one note: the person Marco Rubio’s paid leave plan will help most is Marco Rubio.

Paid leave is an immensely popular policy, with 80% of Americans coming out in favor of paid time off. Its surging popularity, and the increasingly dire situation millions of working families find themselves in, has pushed the issue into the political mainstream. Whereas paid leave was a political pipe dream this time last year, it’s become a centerpiece of the campaigns being run by Democratic presidential candidates Hillary Clinton, Bernie Sanders, and Martin O’Malley.

And the Republican presidential field’s uniform opposition to a federal paid leave policy, and its lack of alternative suggestions, puts it wildly out of step with a vast majority of voters. So Rubio, in taking what is essentially a no-risk position to incentivize paid leave for companies that are already offering it or flirting with the idea of offering it, gets to distinguish himself as the Republican contender who says he values families and means it.

At a moment when the GOP has come to define itself by Donald Trump’s anti-immigrant vitriol and Ted Cruz’s looming threats of a shutdown, Rubio is positioning himself as the even-handed grownup in the room, and that may appeal to establishment Republicans who are kind of freaking out about their party’s presidential prospects.

Rubio’s paid leave proposal could be a big boost for Rubio, but the 26 million private sector workers who don’t have access to any paid time off will need more than a bit of slick campaigning to make ends meet. If they’re looking for a policy that will make that juggling act more manageable, they’ll have to look elsewhere.