(CNN) On Sunday, CNN's Jake Tapper put a very simple question to Alexandria Ocasio-Cortez: How are you planning to pay for the many and various expensive programs and plans that you are either proposing or support? The New York soon-to-be congresswoman didn't have any answers. Like, none.

TAPPER: Your platform has called for various new programs, including Medicare for all, housing as a federal right, a federal jobs guarantee, tuition-free public college, canceling all student loan debt.

According to nonpartisan and left-leaning studies friendly to your cause, including the Center on Budget and Policy Priorities or the Tax Policy Center, the overall price tag is more than $40 trillion in the next decade.

You recently said in an interview that increasing taxes on the very wealthy, plus an increased corporate tax rate, would make $2 trillion over the next 10 years.

So, where is the other $38 trillion going to come from?

OCASIO-CORTEZ: Well, one of the things that we need to realize when we look at something like Medicare for all, Medicare for all would save the American people a very large amount of money.

And what we see as well is that these systems are not just pie in the sky. They are -- many of them are accomplished by every modern, civilized democracy in the Western world. The United -- the United Kingdom has a form of single-payer health care, Canada, France, Germany.

What we need to realize is that these investments are better and they are good for our future. These are generational investments, so that not just -- they're not short-term Band-Aids, but they are really profound decisions about who we want to be as a nation and as -- and how we want to act, as the wealthiest nation in the history of the world.

Tapper pressed, noting correctly that he didn't ask why she believed in making the investments she supports but rather how she would pay for them. Ocasio-Cortez then responded with this: "Well, when you look again at, again, how our health care works, currently, we pay -- much of these costs go into the private sector. So what we see is, for example, a year ago, I was working downtown in a restaurant. I went around and I asked, how many of you folks have health insurance? Not a single person did, because these -- they were paying -- they would have had to pay $200 a month for -- for a payment for insurance that had an $8,000 deductible."

Ocasio-Cortez is making the case that if government took over more aspects of peoples' lives currently controlled by private industry, costs would go down on things like health insurance. So the $40 trillion price tag for her programs would be less.

But again, that isn't an answer on where the money might come from to pay for them. Let's buy into Ocasio-Cortez's case that costs would shrink if the government, rather than the free market, ran things. Let's even say it would halve the costs of the programs that she supports making into law. That's still $20 trillion -- which has to come from somewhere, right?

Tapper is doing an important public service here. He's highlighting the difference between campaigning and governing. The truth is that as a candidate you can be for almost anything because you don't have any responsibility. You aren't in charge of managing the federal budget or reducing our deficit and debt obligations. Free stuff sounds great! But free stuff is almost never free.

This is a problem that Vermont Sen. Bernie Sanders, also a democratic socialist like Ocasio-Cortez, had during the course of his 2016 presidential campaign. According to a study by the Tax Policy Center , Sanders' policy programs would add $18 trillion to the national debt over a 10-year period.

Because Hillary Clinton was seen -- perhaps wrongly -- as the de facto nominee from the jump, the cost of Sanders' many proposals never drew all that much scrutiny. But I talked to myriad Republicans who were almost salivating at the prospect of facing Sanders and picking through the massive costs of what he said he was for.

There's no question that the energy within the Democratic Party is on the left -- from Ocasio-Cortez's upset of Rep. Joe Crowley to Ayanna Pressley in Massachusetts and Andrew Gillum in Florida. But with that raised profile comes raised scrutiny about not just what the likes of Sanders and Ocasio-Cortez believe, but how they will be pay for it.

The truth that Ocasio-Cortez doesn't want to acknowledge is that the only -- or at least the most likely -- way that she fills the gap between cost savings and the actual cost of the programs she is proposing is to raise taxes. Yes, on the wealthy, but also, if we're being honest, on more than just the wealthy.

Raising taxes is never popular. Unless it's someone else's taxes being raised. But if Ocasio-Cortez and Sanders -- and others -- believe that they deserve to lead -- whether in Congress or in the White House -- they need to be candid about both what they are for and how they propose paying for it.

As Jake's interview made very, very clear, Ocasio-Cortez isn't there yet.