(CNN) President Donald Trump has a good point when he rages about America's NATO partners failing to meet even their own burden sharing targets for the alliance's common defense.

And he's only adopting arguments and voicing frustrations expressed by his two most recent predecessors, albeit in a far less subtle, undiplomatic and Trumpian way.

The current President is especially sensitive to the cost of America's security umbrella for its allies, in Asia as well as Europe, and largely sees alliances that underpin US global power in transactional rather than geopolitical terms.

Complaints about NATO spending animated his 2016 campaign, when he branded th e alliance "obsolete" - - so no one in Europe, where years of complacency set in after the fall of the Soviet Union, can say they were not warned.

"It's costing us too much money and frankly they have to put up more money ... we're paying disproportionately," Trump said in a CNN town hall event i n March 2016. At an acrimonious meeting of NATO leaders last year, he said Europe was not being "fair" to US taxpayers. At the disastrous G7 summit last month, Trump slammed NATO as "worse than NAFTA," as first reported by Axios.

But ahead of what is shaping up as a bruising NATO summit in Brussels, Belgium, next week, Trump's anger, expressed in letters sent by the administration to several foreign governments, is raising fears that his hardline approach will backfire and put the alliance itself at risk.

His frustration also seems rooted in a more fundamental hostility to the concept of collective and multilateral cooperation that has united the post-World War II American-led community of democracies.

After all, Trump has a record of pulling out of multilateral arrangements, like the Paris climate accord and the Trans-Pacific Partnership, and he is also railing against the World Trade Organization. He says America's top allies are only interested in raiding its "piggy bank."

So while the President's complaints about Europe's defense spending may be justified, critics fear they are a possible precursor to a splintering of the international system that made the United States the richest, most powerful nation in the history of the world.

Trump's demeanor and "America First" philosophy complicate efforts by leaders like German Chancellor Angela Merkel and British Prime Minister Theresa May to argue to domestic audiences for more defense spending to meet US demands. And if it comes to it, they will have little public support to deploy troops to any Trump-led foreign wars.

Trump's own suspicion of Western institutions may undermine his demands for more spending -- as does his misconception that NATO is like a club to which European members owe billions of dollars in arrears.

And his own commitment to NATO is clouded by his frequent parroting of the talking points of Russian President Vladimir Putin -- whose foreign policy is designed to undermine the West and is viewed as a rising security threat by most of the rest of the 29-member alliance.

One big fear is that Trump could hint publicly that the US will not defend alliance members who fall short of spending targets -- a step that would fracture the notion of collective defense that is central to NATO's identity, and assuredly would delight Moscow.

Obama, Bush complained before Trump even arrived

The tardiness of NATO governments to live up to their own pledges to spend 2% of their gross domestic product on defense and the diminished capabilities of key powers like Britain have long rankled in Washington.

"If we've got a collective defense, it means that everybody's got to chip in, and I've had some concerns about a diminished level of defense spending among some of our partners in NATO," President Barack Obama said in Brussels in 2014.

"The situation in Ukraine reminds us that our freedom isn't free and we've got to be willing to pay for the assets, the personnel, the training that's required to make sure that we have a credible NATO force and an effective deterrent force."

Six years earlier, at his last NATO summit, President George W. Bush had called on NATO members to "increase their defense investments to support both NATO and EU operations," adding: "America believes if Europeans invest in their own defense, they will also get stronger and more capable when we deploy together."

Even without Trump, it was inevitable that Americans would begin questioning commitments abroad and the cost-benefit ratio of alliances like NATO as memories of the horror of World War II fade and the common purpose of the Cold War recedes into history.

But there have been positive signs in recent years, which are likely to be overshadowed by Trump's bristling anger at US allies, with many diplomats fearing that Brussels will see a repeat of the G7 summit in Canada, which Trump blew up, raising doubts about Western cohesion.

The latest NATO figures, from 2017, p oint to a 4.3% increase in defense spending as a percentage of GDP among European alliance members and Canada. Military spending is on the rise among most members -- partly owing to US pressure and renewed fears of Russian expansion following the annexation of Crimea in 2014.

Yet at the point the report was released a year ago, only six NATO nations were spending 2% of GDP on defense, a target all nations have until 2024 to reach.

US complaints run deeper than just the numbers, however.

There is great concern over the capability of NATO armed forces -- as the impact of the Great Recession and budget pressures in nations that fund more generous welfare states than the US have caused some European powers to take painful decisions.

Yet earlier this year, the head of the British army, Gen. Sir Nicholas Carter, warned after years of defense cuts that the capacity of Britain to engage Russian forces battle-tested in Syria and Ukraine could be eroded if efforts were not made to match their capabilities.

"We need to recognize that credible deterrence must be underpinned by genuine capability and genuine commitment that earns the respect of potential opponents," Carter said.

Some US officials are using what they see as foot dragging by NATO members to rebut the claims of Trump critics that the President is trying to undermine the transatlantic alliance -- including by his solicitous relationship with Putin.

"If you think that Russia is a threat, ask yourself this question: Why is Germany spending less than 1.2% of its GNP?" Trump's national security adviser, John Bolton, said on CBS's "Face the Nation" over the weekend.

Complaints that the administration is not committed to NATO are also undercut by its budgeting of $3.4 billion in 2017 for the European Deterrence Initiative , which grew out of an Obama-era program to reassure US partners after Russia's move into Ukraine.

Germany lags in spending

Germany has pledged to raise its defense spending only to 1.5% of its GDP by 2025, despite a string of reports questioning the readiness of its forces. Defense spending has traditionally been a sensitive political topic in a nation that spent decades coming to terms with its militaristic past.

In a letter to Merkel, read to CNN's Michelle Kosinski by a source, Trump said he understands the political constraints that have braked defense spending in her country.

"The US continues to devote more resources to the defense of Europe, where the continent's economies, including Germany's, are doing well and security challenges abound," Trump wrote.

There is also a barely veiled threat that the US will start to question its own devotion to European defense if Europe does not do much more.

"It will ... become increasingly difficult to justify to American citizens why some countries do not share NATO's collective security burden while American soldiers continue to sacrifice their lives overseas or come home gravely wounded."

Such arguments grate among NATO members, given that the only time NATO's Article 5 on collective defense has ever been invoked was in support of the United States after the September 11 attacks in 2001. Nations like Britain and Canada have suffered heavy losses fighting alongside the US in Afghanistan. According to the websit e iCasualties.org, Germany has lost 54 soldiers in the Afghan war. It maintains the second highest troop presence in the NATO coalition in Afghanistan, second only to the US.

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While Trump is furious about NATO spending, there is just as much concern among the alliance partners and NATO supporters in the US that he doesn't even share the common values that underpin the alliance -- or appreciate its vital historic role.

That gulf was emphasized by the resignation this week of the US ambassador to Estonia, J ames Melville Jr. In a Facebook post obtained by Foreign Policy magazine, Melville wrote:

"For the President to say the EU was 'set up to take advantage of the United States, to attack our piggy bank,' or that 'NATO is as bad as NAFTA' is not only factually wrong, but proves to me that it's time to go."

The transatlantic disconnect encapsulated in that post is the reason why the NATO summit next week could be the most crucial in the alliance's history.