Former president Barack Obama famously suggested in a 2016 interview that he questioned a set of orthodox assumptions about American foreign policy that he labelled "the Washington Playbook".

That orthodoxy, widely accepted among American political elites since 1945, includes an unending national commitment to employ America's financial resources and military forces in opposition to any challenges to global peace and stability. The dominant assumption has been that America's broader, enlightened self-interest is best served by a system where peace rules and free trade flourishes.

Mr Obama may have begun the process of reorienting America's global role. But the newly inaugurated Mr Donald Trump is busy shredding the Washington Playbook - as his comments at his inaugural address made clear.

Hearkening back to language not employed in the United States since the 1930s, Mr Trump declared categorically that it is all about putting America's interests first.

Among his most controversial challenges is his questioning of the relevance, utility and cost of the North Atlantic Treaty Organisation (Nato) in the pursuit of America's national security goals. In a somewhat oblique reference to Nato, he said: "For many decades, we've… subsidised the armies of other countries while allowing for the very sad depletion of our military."

Indeed, Mr Trump has repeatedly suggested that Nato is obsolete, most recently in an interview with The Times of London. Mr Trump's logic is simple: America's biggest security concern is terrorism, and Nato is not relevant to that process.

But is Mr Trump correct in asserting that Nato has outlived its utility? Or that Nato's members enjoy a "free ride" on the back of a security umbrella furnished and paid for by the United States?

The first claim is highly questionable. But when we step back from his abrasive tone and language, there is more bipartisan consensus about the second claim among America's political leadership than we might assume.

Let's look at the evolution of Nato, and each claim in turn.

NATO'S CREATION AND GROWTH

Since its founding in 1949 at the dawn of the Cold War, Nato has commonly been regarded as an intrinsically important, stabilising force in the West. Originally composed of a dozen founder members, its initial central task was to deter the Soviet Union and its allies in the Warsaw Pact from invading Western Europe.

The political climate at the time was so tense and Nato considered so important that, in his speech at its founding, President Harry Truman described the new treaty as "a shield against aggression and the fear of aggression - a bulwark which will permit us to get on with the real business of government and society, the business of achieving a fuller and happier life for all our citizens".

But times have changed and so have the circumstances.

At the Cold War's conclusion, Nato's membership spread eastward, incorporating many of the countries that were formerly members of the Warsaw Pact. Today, that number totals 28, with Albania being the latest to join.

IS NATO STILL RELEVANT?

So, is Mr Trump fair in challenging Nato's relevance today? The short answer is "no".

First, Nato forces have been deeply involved in the fight against terrorism. Afghanistan provides the most compelling example.

Article 5, a provision in Nato's original Washington Treaty, stipulates that an attack on any Nato member is an attack on all Nato members. The only time it has ever been triggered was when Al-Qaeda attacked the United States on Sept 11, 2001.

Since then, more than 1,000 non-American military personnel have died fighting alongside US troops in Afghanistan, all but a few of them from Nato countries. If American policymakers intend to fight a global war against extremism, as incoming national security adviser Michael Flynn maintains in his book The Field Of Fight, then Nato would form a cornerstone of that fight.

The second reason for Nato's continued relevance is Russia.

President Trump's repeated assertions that the United States can negotiate a rapprochement with Russia and potentially drop its sanctions against it have met with disapproval in domestic opinion polls.

The idea of forging a working relationship with Moscow in fighting the Islamic State in Iraq and Syria (ISIS) has its attractions for Americans consumed by concerns about terrorism. But the precedents are not good. Mr George W. Bush believed he could work collaboratively with Russia. So did Mr Barack Obama. Both failed. What's more, both Mr Vladimir Putin's and Mr Donald Trump's combustible and confrontational "A-type" personalities don't suggest that either will give an inch when they disagree. So, it isn't outlandish to anticipate a breakdown in that relationship, and a resurgence of Nato's importance in central and eastern Europe if incoming Defence Secretary James Mattis' comments that Russia is the major threat to US interests gains currency in the White House.

SHOW ME THE MONEY

But what of Mr Trump's claims that Nato members are just free riders while America pays for their defence?

Here, there is across-the-board consensus. Both Mr Obama and Mrs Hillary Clinton said the same thing, albeit in more diplomatic language and without the accompanying claim that Nato serves no purpose.

Even Nato's own Secretary General Jens Stoltenberg has recognised the problem and cajoled Nato members to pay more towards the cost of their defence.

The maths is fairly simple.

Each Nato member is supposed to spend 2 per cent of its annual gross domestic product (GDP) on defence. But as its membership has grown, the willingness of the individual members to contribute to the collective defence has conversely waned. That's because as the Soviet threat declined, most European countries engaged in a wind-down of their defence budgets - what's commonly called a "peace dividend". America stopped the wind-down after 9/11. But it's a process that has continued in Europe to this day.

Only five Nato members meet the 2 per cent requirement, including the US, which spends about 3.6 per cent. And of the other four, only Britain could realistically be characterised as having major military capabilities - the remainder being Estonia, Greece and Poland.

Even France, which has Europe's other truly capable force, spent only 1.8 per cent last year. Among the remaining members below the 2 per cent threshold, Germany provides perhaps the most startling example.

Germany has just announced it will increase expenditure - to 1.2 per cent of GDP. What does that tangibly mean? Well, a German Defence Ministry report published at the end of 2015, for example, revealed that only 29 of Germany's 66 Tornado jets were "deployable". The air force had no spare parts for the planes. So, they had to be scavenged from the more than 50 per cent that couldn't be used. A 2014 report by Der Spiegel magazine (which was challenged by the German Defence Ministry) claimed that as few as seven of Germany's 67 CH-53 transport helicopters were fully operational, including those being deployed in Afghanistan, as were only five of its 33 NH-80 helicopters.

Meanwhile, despite the end of the Cold War more than two decades ago, the US deploys huge resources to Germany, and throughout Europe, at considerable cost.

LOOKING AHEAD

There is little doubt that most Nato members have reneged on their financial commitment to an organisation that undoubtedly serves their security interests.

The fact is, however, that Nato has played, and may well continue to play, an essential role in America's national security, whether it is in combating groups such as ISIS or deterring Russian aggression in central and eastern Europe.

Maybe the incoming president's criticisms are simply a ploy to get Nato members to pay more. Maybe these countries will succumb to pressure. Let's hope that is all it is. Because neither America nor Europe will be more secure without Nato.

•Simon Reich is professor in the Division of Global Affairs and the Department of Political Science, Rutgers University Newark.

•This article first appeared in theconversation.com, a website of analysis from academics and researchers.