London(CNN) European leaders are subjecting President Donald Trump to a crash course in history, hoping to use D-Day commemorations to shake his skepticism about alliances that have kept global peace for three-quarters of a century.

The President saw for himself on Thursday the human price paid by thousands of Americans buried under poignant, regimented rows of white gravestones overlooking the beaches they stormed under curtains of Nazi fire on June 6, 1944.

Their sacrifice in the Normandy landings helped purchase 75 years of European freedom and prosperity, and enshrined America as the leading world power and guarantor of Western democracy.

During the President's three days in Britain built around D-Day observances, it became clear that his interlocutors hope he will gain a new appreciation for how American engagement and common sacrifice built a postwar age that benefited millions but is now under threat from outside forces -- and incredibly, from the President of the United States himself.

Queen Elizabeth II, British Prime Minister Theresa May and German Chancellor Angela Merkel have all stressed the need to maintain alliances increasingly under pressure from internal populist forces and rising competition in the East.

"As we face the new challenges of the 21st century, the anniversary of D-Day reminds us of all that our countries have achieved together," the Queen said, mixing hospitality with a history lesson at a state banquet in Trump's honor.

"After the shared sacrifices of the Second World War, Britain and the United States worked with other allies to build an assembly of international institutions to ensure that the horrors of conflict would never be repeated," said the Queen, one of the few heads of state still alive who remember World War II.

"While the world has changed, we are forever mindful of the original purpose of these structures: nations working together to safeguard a hard-won peace," she added.

The President heard the appeals. But the question now must be whether he got the message, and will understand the deep concerns raised in Europe by his conduct and rhetoric.

Trump, with his "America First" rhetoric, has made clear that he believes that the sovereignty of individual nations pursuing their own interests should be the basis for international relations instead of formal multilateral institutions. That doesn't preclude alliances but is a looser affiliation than the interdependent model preferred by many European leaders.

In a moving oration at the service, Trump chose to dwell more on the tales of awe-inspiring courage and self-sacrifice from individual American soldiers thousands of miles from home -- than address the sweeping historical points and geopolitical arguments made by his European counterparts.

"You are the glory of our republic, and we thank you from the bottom of our hearts," Trump said at the Normandy American Cemetery in northern France.

"You are among the very greatest Americans who will ever live," Trump said.

But the President also offered a strong endorsement of the transatlantic alliance -- in a way that may go some way to easing anxieties on the European side of the ocean about his attitude towards US alliances.

"Our cherished alliance was forged in the heat of battle, tested in the trials of war, and proven in the blessings of peace," Trump said at the 75th anniversary of D-Day.

"Our bond is unbreakable," Trump said.

There are risks to Europe's tendency to school Trump, since he is not one to take lectures kindly and cannot bear the perception that his gut-led leadership is being managed. For proof, consider the tense relations he had with former Cabinet members such as James Mattis and Rex Tillerson.

There's also little evidence that the flattery piled on Trump by other world leaders is especially effective in getting him to shed idiosyncratic and deeply held beliefs -- even those that confound facts and logic.

On the eve of the observances, Republican National Committee Chairwoman Ronna McDaniel criticized news coverage of the President's trip in an appearance on Fox Business Network.

"I just have a reminder for the media: He's your President too," she said. "This is our President. This is our country. We are celebrating the anniversary, 75 years of D-Day.

"This is the time where we should be celebrating our President, the great achievements of America, and I don't think the American people like this constant negativity. There are times when we should be lifting up our President, especially when he's overseas."

The ambivalence of a President

Europeans see the trans-Atlantic alliance as an indispensable structure ensuring their security that can prolong three-quarters of a century of liberty and free market economics.

Trump's ambivalence comes at an especially sensitive geopolitical moment, as powers such as China and Russia challenge the Western-led order and offer alternative development models for strongmen leaders who reject universal values.

It may be no coincidence that Russian President Vladimir Putin and Chinese President Xi Jinping are meeting just as Western leaders head to France.

Unique among post-Cold War presidents, Trump ditched the traditional view of NATO and the European Union as institutions that bolster the US-led order and multiply American power.

The former real estate tycoon takes a more transactional view of such bodies, making hard-nosed calculations about the material return on US investment -- in strictly financial terms.

Many Presidents have griped that the allies have failed to share the burden of the NATO umbrella and about the failure of many to live up to their own defense spending goals.

But Trump is the only commander in chief to make such complaints an organizing principle of foreign policy -- a strategy mirrored in his attitude toward Asian allies Japan and South Korea.

He left NATO leaders visibly shocked at his first visit to the alliance headquarters in May 2017, claiming that some allies "owe massive amounts of money from past years."

Trump, either deliberately or by omission, often ignores the fact that the defense spending target of NATO members -- 2% of their gross domestic product -- is not a dues payment to the alliance.

In pictures: President Trump in Europe US President Donald Trump, visiting the Normandy American Cemetery in France, participates in a ceremony to commemorate the 75th anniversary of D-Day on Thursday, June 6. Trump and his wife, Melania, visit the graves of troops who died on D-Day. The Trumps are joined by French President Emmanuel Macron and his wife, Brigitte, as they watch a flyover on June 6. A World War II veteran shows Trump a photo of himself with the President. Trump addresses the commemoration ceremony in France. Macron and Trump embrace during the D-Day ceremony. A World War II veteran looks over Trump's shoulder during the commemoration ceremony. At a D-Day event held Wednesday, June 5, in Portsmouth, England, Trump reads a prayer that President Franklin D. Roosevelt gave over the radio on D-Day. Trump heads back after speaking at the event in Portsmouth on June 5. Britain's Queen Elizabeth II and Prince Charles play host to the Trumps at the D-Day event in Portsmouth. British Prime Minister Theresa May is at left. Trump meets with German Chancellor Angela Merkel on the sidelines of the D-Day event in Portsmouth. The Trumps pose for a photo ahead of a dinner at Winfield House in London on Tuesday, June 4. Joining them, from left, are Woody Johnson, the US ambassador to the United Kingdom; Camilla, the Duchess of Cornwall; Prince Charles; and Johnson's wife, Suzanne Ircha. Trump and Prince Charles share a toast at Winfield House. Trump and British Prime Minister Theresa May speak at the dinner on June 4. Melania Trump spends time with Camilla and Suzanne Ircha, the wife of the US ambassador. Brexit Party leader Nigel Farage, center, arrives at Winfield House, where the Trumps are staying during their visit. Trump and May give a joint news conference on June 4. "I think she's done a very good job," Trump said, reversing past critiques of her failure to strike a Brexit deal that both Parliament and the EU can accept. Trump and May are followed by their spouses as they make their way to the news conference in London on June 4. The President offered plenty of praise for May, who recently announced her resignation. Philip May and Melania Trump attend a garden party at No. 10 Downing Street. Larry, the No. 10 Downing Street cat, sits underneath The Beast, the presidential armored Cadillac. Trump speaks opposite May at a business roundtable discussion in London. Trump stands next to Queen Elizabeth II before a state banquet at Buckingham Palace on Monday, June 3. Joining them are Melania Trump, Prince Charles and Camilla. The state banquet had a few hundred guests, including several of Trump's children. Trump and the Queen laugh during the state banquet. The Trumps tour Westminster Abbey on June 3. The President signed the guestbook at Westminster Abbey. "Thank you so much," his message said. "This has been a great honor. Special place." The Trumps are joined by Prince Andrew as they pay their respects at the Tomb of the Unknown Warrior in Westminster Abbey. The President's convoy drives down Pall Mall in London on June 3. Queen Elizabeth II welcomes the Trumps to Buckingham Palace. She took them on a tour of the royal collection. Among the items on display was "American Pewter Thoroughbred," a gift that Trump gave the Queen last year. Trump inspects a guard of honor at Buckingham Palace. The US National Anthem is played during a welcoming ceremony at Buckingham Palace. From left are Melania Trump, the Queen, Trump, Charles and Camilla. British Army troops fire a cannon in London's Green Park to mark the beginning of Trump's visit. The Queen greets the President as he arrives at Buckingham Palace. Prince Charles greets Trump as he steps off Marine One at Buckingham Palace. The Trumps are welcomed in London by Charles and Camilla. Trump's daughter Ivanka, who is also advisor to the President, looks out of a window at Buckingham Palace. People outside Buckingham Palace photograph the Changing of the Guard ahead of Trump's arrival on June 3. The Trumps arrive at Winfield House, the residence of the US ambassador, on June 3. Amnesty International installs "Resist Trump" banners on Vauxhall Bridge in London. Marine One flies past the BT Tower in London. The Trumps walk toward Marine One after arriving at London's Stansted Airport on June 3. The President salutes troops as he and the first lady arrive at Stansted Airport. Trump is greeted by UK Foreign Secretary Jeremy Hunt after arriving at the airport. The Trumps arrive at Stansted Airport.

It took several tries for Trump to eventually affirm NATO's principle of mutual self-defense. His grudging manner did little to quell concerns about his attitude toward the group.

His odd deference to Putin, who has made undermining Western democratic institutions a centerpiece of his rule, also rattled European leaders.

For decades, presidents such as Ronald Reagan and Barack Obama have used the imagery of the Normandy invasion to stress bonds between allies united in a cause greater than individual nation-states.

Trump's mind, which revolves around constant win-loss evaluations, does not work that way.

He has, in the past particularly, balked at lectures on alliance solidarity from Germany's Merkel -- perhaps his least favorite leader of a major European power.

Trump has been been infuriated that Germany, the top European economic power, has yet to meet its 2% spending benchmark. His criticism often insults Germans, given the still-raw sensitivities about militarism in the country 74 years after the end of the Nazi era.

Trump and Merkel had a short meeting in Portsmouth, in southern England, on Wednesday, where she attended eve of D-Day events -- to show how European fractures have healed in the postwar world nurtured by American leadership.

She told reporters the invasion "demanded incredible sacrifices of hundreds of thousands of soldiers ... it led to something that we can be proud of today, namely reconciliation, unification within Europe, but also the entire postwar order that has now brought us peace (for) more than seven decades."

Trump's defenders argue that he's not opposed to all this -- he just wants everyone to pay their fair share to maintain it -- a point the President hammered home yet again while meeting May on Tuesday.

"To address today's challenges, all members of the alliance must fulfill their obligations. They have no choice. They must fulfill their obligation," the President repeated, for emphasis.

The White House has also posted fresh US troop deployments to Western Europe as proof of his fealty to the alliance.

'A liberation like few people have seen'

In the run-up to the commemorations of D-Day, when more than 160,000 allied troops crossed the English Channel in the largest invasion force in history, Trump has expressed admiration for the scale of the task faced by the allies' armies.

"It was a liberation like few people have seen before," he said."Among them were more than 130,000 American and British brothers-in-arms. Through their valor and sacrifice, they secured our homelands and saved freedom for the world."

But his fellow allied presidents and prime ministers will be holding their breath to see how Trump interprets the lessons of D-Day on Thursday and fits them into his own worldview.

Some leaders have taken to offering Trump exaggerated praise for eking more defense spending out of European governments -- even though the 2% target sets a 2024 deadline and some of the new investment predated his presidency.

"Thanks in part to your clear message on burden sharing, Donald, we have seen members pledge another $100 billion, increasing their contributions to our shared security," May said Tuesday.

The British leader also tried a new tactic -- trying to impress Trump, who is a fan of bristling new hardware, with Britain's new capabilities that are coming online despite years of crimped military budgets.

"I'm pleased to announce that NATO will soon be able to call on the UK's Queen Elizabeth-class aircraft carriers and F-35 fighter jets to help tackle threats around the world," May said.