Hillary Clinton, recently, has taken to pointing this out.
"His plan depends upon governors like your governor putting in a lot of money," she said recently while campaigning in Wisconsin. "Now, I've got to tell you, having followed from afar the wrecking ball that Scott Walker has used against higher education, I don't think it's all that realistic to say, well, you'll get free college as long as Scott Walker chips in about, you know, yes, about $300 million."
Sanders's reply to this, when asked by CNN's Erin Burnett, was to misdescribe the essential elements of his own plan.
Now, what Secretary Clinton says is that Scott Walker may not go along with that. But you know what happens to the state of Wisconsin if he does that? California will, Vermont will, states all over this country will, and young, bright people will be leaving Wisconsin. And I think the people of Wisconsin will tell Scott Walker, you know what, this will be a disaster for the future of our state. Because when kids leave, sometimes they don't come back. So I think the idea is sound.
How Sanders's plan actually works
What Sanders's plan, as spelled out in his College for All Act, does is provide federal matching grants to help defray the costs of eliminating tuition for in-state students.
Specifically, he is offering a 2-to-1 federal match for states that do this along with meeting a few other criteria like reducing reliance on adjunct faculty. This is a sufficiently attractive offer that some states would probably go for it. But it's going to cost a lot of money, and tax-averse Republican governors like Walker pretty clearly aren't going to do it.
Sanders implies that Wisconsin students will just head to blue states like California instead.
But his plan doesn't provide California with any money to cut tuition for out-of-state students. And by increasing in-state enrollment at California universities, Sanders's plan would almost certainly make it harder for Wisconsinites to get into public schools in California.
And that's assuming California does it! Most states — including California and Vermont — have cut higher education spending in recent years, and federal matching money may not make that up.
Massive political change is hard
The bottom line is that electing Bernie Sanders president is not going to eliminate tuition for most American college students. Not because Sanders's College for All bill probably wouldn't pass even if he did win, but because even if it did pass the bill simply will not lead to the elimination of tuition in most cases.
This isn't Sanders's fault, per se — it's not sloppy legislative drafting — but it reflects the fact that the administration of public institutions of higher education in the United States is primarily a state matter.
The federal government has a role, and it's an important one, but it's secondary. The fiscal cost of a total federal takeover of the system would be so prohibitive that Sanders doesn't propose it, and that means his ideas can have only a limited impact on what happens on the ground.
That's all fine, except Sanders's rhetoric is raising expectations and mobilizing voters around promises of change that are completely at odds with what his policies and American institutions can actually deliver.