Politics is something of a circle and, while appearing poles apart, the distance between left and right can occasionally push them close together in surprising ways.

Nowhere highlights this better than the US over the past few years.

Donald Trump beat Hilary Clinton in part because his economic policies on the right appealed to white, working-class, older males.

It is quite possible Bernie Sanders could have beaten Mr Trump, in large part because his left-wing economic policies might have appealed to those same voters Mrs Clinton's middle-of-the-road proposals didn't resonate with.

In fact, the gap between Mr Trump and Mr Sanders' economic policies is not as large as may at first seem apparent.

Mr Trump promised greater protectionism (which he has so far delivered) and massive economic stimulus through corporate tax cuts (also delivered) and infrastructure spending (not delivered yet).

Mr Sanders also wanted more infrastructure spending, in addition to increased public spending on social security and health care, and free public tertiary education — all economically stimulatory spending.

In contrast to Mr Trump, Mr Sanders wanted higher taxes on the wealthy but, like Mr Trump's, his plan was widely considered likely to blow out the budget deficit.

Governments get their money for nothing

Why worry about budget deficits when you can print your own money, argue Modern Monetary Theorists. ( Reuters: Jim Young )

So, both Mr Trump and Mr Sanders were proposing stimulatory economic policy at a time when the US economy was already at, or near, what economists consider full-employment, something that most economists warned might trigger runaway inflation.

Most economists, but not Bernie Sanders' senior economic adviser, Stephanie Kelton.

The economics professor from Stony Brook University in New York treads an unusual path between advising a number of left-leaning Democrats and holding the ear and support of a number of Wall Street financiers.

Economist Stephanie Kelton ( Supplied: Twitter )

She is one of the world's leading proponents of "modern monetary theory" (MMT) — an economic theory that, essentially, argues budget deficits simply don't matter, because most governments print their own money.

"In the modern era, governments spend by instructing their bank — the central bank — to change the number in a seller's bank account," she tells me in an interview.

"If the government spends a 100 into the economy, but it only taxes 90 back out, well we record a budget deficit on the Government's books, we write a -10.

"But that's only half the picture. What you have to do is focus on the fact that when the Government puts 100 in and only takes 90 out, somebody ends up with 10 that they wouldn't have otherwise had."

Professor Kelton argues excess money the Government is releasing into the economy ends up buying the debt the Treasury is racking up.

"The money to buy the bonds is already in place because the Government has run the budget deficit," she explains.

"The national debt is nothing more than the money that the Government spent into the economy, didn't tax back and is currently being held — saved — in the form of treasuries."

Trump's trillion-dollar 'perfect example' of MMT

The Trump administration's tax cuts have driven the current US budget deficit up to $US779 billion ($1,079 billion), because the Government didn't try to recover much of the lost revenue elsewhere.

That's why Professor Kelton describes Mr Trump's tax cuts as a "perfect example" of modern monetary theory in action, albeit she thinks misdirected at high-income earners and large corporations who will tend not to invest the money in building economic capacity and social welfare.

"At the time that the Republicans were looking at these big tax cuts, many Democrats were saying, 'Hold on, you can't do this, you don't do this when the economy's already at full employment, you don't do stimulus at full employment'," she recalls.

"Well, they did it and guess what happened?

"US real GDP growth ticked up, the unemployment rate went down, we didn't cause an inflation problem, and so you got some modest improvements in the way the US economy is progressing and nothing dangerous has happened as a result."

Professor Kelton argues the effects of Mr Trump's policies provide proof the US Government should have done much more, much sooner to drag the economy out of its Great Recession in the wake of the financial crisis.

During the global financial crisis, the Obama administration spent $US787 billion in stimulus to boost the economy, but some advisers were advocating for $US1.8 trillion.

Professor Kelton says Mr Obama should have listened to them.

"There just wasn't the appetite — the administration and really too many Democrats were afraid that because the deficit had increased as a result of the weak economy, that they weren't courageous enough to take another vote to add to the deficit with another round of fiscal stimulus," she said.

Is there a limit to government spending?

Professor Kelton doesn't want to give the impression governments can spend without restraint simply because they control the purse strings.

Of course, some countries don't actually control their own currency or monetary policy, with the eurozone the notable example.

But, even for those that do, Professor Kelton says inflation and interest rates could run out of control if a government tried to generate more economic activity than its country had the natural or human resources to cope with.

But she argues that doesn't mean there needs to be a "reserve army" of unemployed, as Marx labelled them, in order to keep wage rises and inflation under control.

Professor Kelton and other MMT devotees advocate for genuine full employment through a job guarantee instead.

"There's a better way to avoid inflationary pressure — to anchor prices — and it's through employing people at a base wage in public-service employment," she explains.

"What you get is essentially a buffer stock where, when the economy is in recovery and the private sector wants to hire those people out, they move out of the pool of government-employed workers, and when the economy begins to weaken, the buffer stock employs them back in government work.

"So it's actually price stabilising."

Likewise, she plays down suggestions her policy proposals might scare investors, who might invest the cash a deficit government is pumping out in other countries with tighter fiscal policies.

"This is exactly the kind of program that is reassuring to business because you're signalling to business that you're going to maintain aggregate demand," Professor Kelton said.

"You're going to maintain an economy with people who are employed, who have incomes, who are going to be there to be good consumers. This is exactly the kind of policy that ought to attract capital."

Given the patronage she's enjoyed from some key financial figures, it's clear some on Wall Street agree.

Professor Kelton has been invited to Australia by organisation GetUp! and is speaking as part of its Rethinking Our Economy roadshow.