How insane, how truly nuts, is it that Donald Trump is actually the presumptive nominee of a major party for president of the United States?

So nuts that The Donald has finally come out with his Big Plan for the Economy: Let’s make like Greece and default on the national debt. Put this on a cheap hat: Let’s Make Greece Great Again.

Speaking on CNBC on Thursday, Trump floated his plan to deal with the national debt: Ask creditors to take a haircut, or a reduction in the face value of their debt, which is a default, in exchange for … what exactly? Well, exactly nothing. But thinking has never been a prerequisite for speaking in Trumpland.

“ Doing things on purpose that endanger all Americans’ access to credit is beyond crazy. Done consciously, it’s borderline treason. ”

Reaction is as disbelieving as it was in 2011, when first-term Tea Party Florida congressman Ted Yoho called on the financial experience he amassed as a large-animal veterinarian to opine that it would be smart to default on the national debt to show bond markets we’re serious about getting our fiscal affairs in order.

“No one on the other side would pick up the phone” if Trump tried to renegotiate the debt, Wrightson ICAP chief economist Lou Crandall told The New York Times. “Why should they? They have a contract.’’

Let’s count what’s wrong with this lamebrained idea. (The 600 words left in this column shan’t be enough.)

1. You say you’ve done this before, Mr. Trump, but how did it turn out?

It’s incomprehensible that, decades after Trump began to go through bankruptcies, debt restructurings and the like, he hasn’t figured out that those deals ended with him being stripped of control of assets he spent years trying to build up.

Yes, his creditors wrote down debt at the Plaza Hotel. They also booted him out. Yes, his creditors restructured and wrote down debt at Trump’s casino companies, and he hasn’t controlled them in years. Same thing at his giant Riverside South development on Manhattan’s West Side. It’s why Trump would have been better off putting Dad’s dough in an index fund way back when.

Obama on Trump: The presidency is not a 'reality show'

Mr. Trump, your creditors reduced your debt in order to get you to go away. Did you miss that? As president, you’ll have a four-year term and won’t be able to offer them that.

2. What happens to everyone else when they default on their debt?

In Florida, a state Trump ain’t winning the election without, lots of people who tried this genius plan with mortgage lenders lost their homes. One reason the economy has been so slow is that they were so scarred by the experience, they moved in with their parents and didn’t leave for years — low rates of household formation held down the whole economy until the last year or so.

Superpowers can’t go live in Mommy’s basement.

Short of that, miss a credit card payment by 30 days even once and see what happens. The card issuer will slap on a penalty rate, often in the high 20% range. And, in many cases, the missed payment will add half a percentage point even to a mortgage from an unrelated bank.

With a national debt of $19.2 trillion, that half a point would add hundreds of billions of dollars, at least, to what we spend on interest each year. But most late credit card payments are mistakes: The consequences would likely be worse if the U.S. defaulted on purpose. And higher interest rates on existing loans would just be the beginning.

3. How’s Greece doin’?

Sovereign debt crises rebound throughout economies, making it hard to get credit for governments, individuals and companies alike. It’s part of what has happened in Greece, currently sporting a 25% unemployment rate, and even Americans got a fair taste of it in 2008 and afterwards.

We lived through that: Car sales falling nearly in half, 8 million jobs lost in a few months, and the disastrous election of, depending on one’s politics, Barack Obama to the White House or Ted Yoho and 60 just like him to Congress two years later. If new credit just to the government were sharply cut, as it was in Greece, the consequences of balancing the budget immediately would be measured in millions of jobs.

Which bothers Trump not. In the same interview, he advocated boosting spending on infrastructure to exploit the very low interest rates his other actions would end. He also wants to cut taxes by $12 trillion. As the kids say, SMH.

Doing things on purpose that endanger all Americans’ access to credit is beyond crazy. Done consciously, it’s borderline treason.

Lest we forget, Ted Yoho and Co. helped send the S&P 500 Index 20% lower by rattling confidence during the 2011 debt showdown. Apparently, that was just a warm-up act.

It sure does make Trump’s vice presidential selection process simpler, though. The only choice: former Greek Finance Minister Yanis Varoufakis.

Tim Mullaney writes about economics and politics for MarketWatch.