The Affordable Care Act leaves today's Democratic presidential contenders at something of an impasse. With Barack Obama having finally passed the top item on the liberal policy wishlist of the last 60 years, what comes next?

Protecting, expanding, and improving ObamaCare is one obvious goal. But when it comes to fresh policy, the party appears to be uniting around something else: state-funded pre-K, the focus of a new bill to be proposed soon, as Greg Sargent reported Monday.

In itself, pre-K is a worthy goal. However, as so often with Democrats, the policy itself is distinctly weak tea — especially for a benchmark proposal that has zero chance of passing. On both policy and tactical grounds, they would be well-advised to aim a lot higher.

So what's in the plan? Sen. Bob Casey of Pennsylvania is introducing it as an amendment to the upcoming reauthorization to No Child Left Behind, and it is very similar to the pre-K bill he introduced back in 2013. The full details aren't yet forthcoming, but we do have a sense of the basics.

The bill allocates over $30 billion in matching block grants to states that provide good preschool for four-year-old children whose families are at or below 200 percent of the poverty line. If a state already has such a program set up, it can expand access to three-year-olds with similar conditions. States can also provide subgrants to other institutions to expand pre-K, subject to a host of quality conditions.

All that is paid for by limitations on corporate "inversions," in which companies move their legal jurisdictions to escape U.S. taxes. Casey would require such companies to be at least 50 percent foreign-owned to qualify, as compared to the current 20 percent.

This would be a big improvement on the status quo. Pre-K programs have shown generally good results for children (though not always or in all circumstances). Perhaps more importantly, at a time when both parents generally have to work to make ends meet, child care is an increasingly burdensome expense. When a child reaches school age, it is a huge relief for many families. That's why the universal pre-K program in very conservative Oklahoma (passed by a combination of coincidence and trickery) is now unshakably popular.

But there are several big problems with Casey's proposal. First, unlike in Oklahoma, it is means-tested, meaning it takes into account whether families are financially eligible. This is probably to make the proposal cheaper and more sensible-sounding. But that comes at a high price: limiting the benefits of the proposal to the politically weak. In an age of economic weakness, poor-only benefits face heightened suspicion and resentment — just compare how Republicans speak about food stamps (means-tested) to how they speak about Social Security (universal).

Second, it's block-granted, meaning the states are in charge. This will work fine in the blue states, which will eagerly jump at the chance to expand education. It will most likely be ignored for decades in the red states, which need the benefits a lot more.

In short, it's both weak policy and politically unstable. There's a reason why conservative anti-welfare political strategy starts with block-granting and means-testing — because it makes the programs easier to kill off. Traditional welfare was basically destroyed in this way.

It also goes against the very idea of public education in the first place. School is not just about creating higher-skilled economic cogs to make the national income increase faster. It's also about creating a mass culture and a well-rounded citizenry. About 90 percent of American children attend public school, which helps at least somewhat in creating an inclusive sense of American identity and social cohesion. This would be a very different country if only poor children got public education, and everyone else had to pay for it privately.

Finally, there is the general issue of tactics. I could see supporting this as a compromise proposal, but not as the first proposal out of the gate. If the bill is doomed (as Ed Kilgore explains, it is), then why not plant one's flag way further out? Just copy-paste Oklahoma's stronger version, for instance. Or have the federal government itself operate an opt-in pre-K program. Stick in some federally paid child leave, and bundle up our goofy array of child tax credits into a universal child allowance while we're at it.

All that likely won't pass. But this is a long-term political project we're talking about here. Making a big policy ask will prime the political debate and leave space for future compromise, if necessary. But if one starts right in the middle of the policy spectrum, chances are good that the proposal will eventually be whittled down to nothing.