The latest brainstorm being cooked up by the Democrats — to do away with the hundred-dollar bill — is front-page news all over the world. And for good reason. It’s a terrible idea, and not only because the c-note is the most popular form of green.

Banning the Benjamin would strip Americans of a layer of privacy and a currency of convenience. It’s being advanced as a war measure to make it harder for terrorists to carry cash. But it’s a smokescreen for the fact that the Democrats are out of ideas on both the economy and national security.

The putsch against the Benjamin is being sprung by Lawrence Summers. He was President Bill Clinton’s treasury secretary and also a president of Harvard. He came within a whisker of being chairman of the Federal Reserve under President Obama.

Mr. Summers wrote up his idea in the Washington Post, touting a proposal from a think tank he directs. It wants the Europeans to stop issuing new 500-euro notes and America its hundreds — and maybe even withdraw such notes already in circulation.

This, Mr. Summers suggests, is justified because these denominations — and Portraits of Grant (meaning 50s) — are being used by criminals and terrorists. In “certain circles,” Mr. Summers says, the 500-euro marker is known as the “bin Laden.”

That strikes me as an unconvincing argument, particularly from the Democrats. They have withdrawn from nigh every front in the war on Islamic terror. They don’t want to name our enemies or even call our struggle a war.

Meantime, they’re downsizing our army. Secretary of State Kerry is preparing to surrender in Syria, and the Russians and Communist Chinese are on the march. The best the Democrats can come up with is taking away Americans’ favorite form of cash.

It’s the financial equivalent of gun control. When criminals use guns the Democrats want to take guns from law-abiding citizens. When terrorists use hundreds, the liberals want to deny the rest of us the Benjamins.

Ordinarily this would invite ridicule, save for the fact that it’s part of a larger game — the movement to do away with cash altogether. This movement is growing by the year, at home and abroad.

Just this month, the American editor of the Financial Times, Gillian Tett, issued a column on the benefits of doing away with cash. She quoted the head of Germany’s biggest bank as predicting that in a decade “cash probably won’t exist.”

What the government fears is that if people use cash, they’ll be able to act privately. It’ll be harder to impose on them the sky-high taxes the government likes. It would never occur to a government official to deal with this problem by, say, lowering taxes.

Nope, they just want to make it harder to use cash. Mr. Summers actually argues that one reason to do away with high-denomination banknotes is that $1 million, carried in the form of 500-euro notes, weighs only 2.2 pounds.

If a terrorist were forced to lug around his million in 20s, it would weigh 50 pounds. This is what they’re teaching up there at Harvard these days.

By that logic they’ll soon be arguing in favor of going back to using gold bullion. At the price of gold under the post-war gold standard, after all, $1 million would weigh 1,959 pounds. Having to lug that around would really slow down the terrorists, but they don’t like anything that smacks of the gold standard up at Harvard.

Welcome to the age of modern money. First the government runs down the value of the dollar. Then when people start easing their backs by carrying what little money they have in hundreds, the Democrats start complaining about terrorists.

The truth is that the Democrats aren’t worried about the terrorists. (Apple won’t even unlock a cellphone to help the government catch terrorists.) If the Democrats are so worried about terrorists, why are they preparing to give $150 billion back to the Iranians?

Then again, how about this for a plan? President Obama can use the government’s stock of hundred-dollar bills to pay off the Iranians. As soon as the cargo planes are in the air, Congress can pass a law saying Benjamins are no longer legal tender.

Why, it could be the start of real monetary reform.

This column first appeared in the New York Post.