California's new Gov. Gavin Newsom (D) has a big idea: Six months of paid leave every time a family in the state has a child. It's a piece of groundbreaking legislation that, if passed, could become a demonstration project for paid parental leave laws across the country.

First, the details. Newsom was sworn in Monday morning as California's new governor and he needs to deliver his first budget proposal to the state legislature by the end of this week. Sure to be included are at least some of his campaign proposals to help families in California cope with the costs of child care and education, like early childhood education programs and more affordable college. But the big ticket item is his paid parental leave expansion.

According to The New York Times, Newsom's team intends to include a plan in the budget to give every Californian six months of paid parental leave from work when they have a child. They haven't fully fleshed the details out yet, and instead are setting "a goal of ensuring that all newborns and newly adopted babies can be cared for by a parent or a close family member for the first six months." There is also a task force planned, to hash out questions like whether the paid leave can be split between two parents, or whether it could also go to an extended family member who steps in to help (in the case of a single-parent home, for instance). The new level of paid leave would also be phased in over several years.

To get a sense of what a big deal this is, consider that California already has the most generous paid parental leave law in the country, and it only offers three months — half of what Newsom is proposing.

A handful of other states also offer three months of paid leave, and a few offer less, while the vast majority of states don't offer any paid leave at all. At the national level, federal law says that employers must give their workers three months of unpaid leave, but that's it. In the European Union, by contrast, new mothers get a minimum of three and a half months, and new fathers get paid parental leave under plenty of circumstances as well.

Private American employers are, of course, free to offer paid child leave on their own initiative. Some of the biggest companies offer four months, all the way up to a year in some rare cases. But overall, only 16 percent of U.S. workers get paid child leave through their job. Meanwhile, 71 percent of women with children are either working or looking for work, and two-thirds of families with children have both parents in the labor force.

Opponents argue that paid parental leave is a drag on business growth. But research actually found that the policy has no impact on companies or that it could even improve productivity a bit. And that's on top of the improvements to well-being that paid leave brings for mothers, fathers, and their children.

With over 12 percent of the American population, and over 13 percent of its economic output, California would provide a unique opportunity to demonstrate all the benefits of generous paid parental leave policies to the nation.

In fact, 82 percent of Americans already support paid leave for new moms, and 69 percent support it for new dads. These massive numbers go a long way towards explaining why, of the few states that do have paid leave, several passed it in just the last few years. And in last year's election, 29 percent of political candidates for either Congress or state governorships stumped for some form of paid parental leave in their campaigns — a wild increase from a mere 4 percent four years ago.

The trick, of course, is how to pay for it.

For the all the stereotypes about California being solid blue, Newsom is dealing with a state that's pretty ornery when it comes to taxes. Super majorities are required in the state legislature to pass any tax increases. And while Newsom and his party technically have those super majorities, plenty of California Democrats will be loath to pass a tax hike, even for a policy this popular. Right now, the most Newsom's team is proposing is to use some administrative moves to open up money in the budget, but they'll ultimately need more funding.

The most likely option is a payroll tax that either hits employers, or employers and employees equally. That's how California's current paid leave law is funded, it's how Washington state paid for its version of the policy, and it's what the FAMILY Act — a paid parental leave bill proposed at the national level — would do.

Of course, California and other states could use deficits to finance a paid family leave law as well. The first problem is that, right now, every state but Vermont has a balanced budget requirement. States also don't have the same monetary and fiscal powers as the federal government, so they must keep their deficit spending within limits (though they generally have more freedom than they allow themselves).

The other thing supporters could consider is how to help out states at the national level. Reviving something like revenue sharing could use the federal government's fiscal prowess to give states more room to spend on these sorts of progressive priorities.

Ultimately, the most straightforward political strategy would probably be to get California's expansion passed, and then use that to justify passing the FAMILY Act or something similar nationally.

But progressives should also keep as many paths to paid family leave open as they can.