David A. Andelman, editor emeritus of World Policy Journal and member of the board of contributors of USA Today, is the author of " A Shattered Peace: Versailles 1919 and the Price We Pay Today ." Follow him on Twitter @DavidAndelman . The views expressed in this commentary are his own.

(CNN) On the Fourth of July in 1821, Secretary of State John Quincy Adams delivered a remarkable statement of American foreign policy that resonates as vividly today.

The United States "goes not abroad in search of monsters to destroy. She is the well-wisher of freedom and independence of all," said Adams, who four years later would become the nation's sixth president.

Then he added, "She has a spear and a shield: but the motto upon her shield is, Freedom, Independence, Peace."

For the next two centuries, through two World Wars, Adams' pronouncement has been a controversial view in a central battle of American foreign policy -- the tension between realists and idealists.

Woodrow Wilson, our 28th president, persuaded a reluctant Senate to take the United States into a war in Europe. He felt the need to issue 14 reasons why the nation had to enter a bloody conflict on a far-away continent that for many Americans seemed no business of its own.

Now it is up to America's 45th president to persuade the nation and the western world to follow him over another, perhaps equally steep, cliff. Donald Trump, who throughout the campaign and the early weeks of his presidency has played the realist to Hillary Clinton's idealist, is suddenly seeking to convince allies and the United Nations that they need to take up arms in the interest of what is right and good.

His transformation has been stunning. "For many decades," he told the world in his inaugural address on January 20, "we've defended other nation's borders while refusing to defend our own," adding an assurance that "from this moment on, it's going to be America First."

It was a theme he'd repeated since he raised the concept in his first major foreign-policy address one year ago: "My foreign policy will always put the interests of the American people and American security above all else. That will be the foundation of every single decision that I will make."

And that seemed to resonate with his followers. But at around 9:40 Thursday night, a whole new Trump seemed to emerge suddenly from the shadows.

"My fellow Americans," he began. "Tonight, I ordered a targeted military strike on the airfield in Syria from where the chemical attack was launched." And then came the plea, "I call on all civilized nations to join us in seeking to end the slaughter and bloodshed in Syria. And we hope that as long as America stands for justice, then peace and harmony will, in the end, prevail. Goodnight. And God bless America and the entire world."

Some commentators pointed out that this was Trump's first blessing of the entire world. But in any event, it was certainly a new vision of America First.

It is hard to imagine Trump bearing John Quincy Adams' spear and shield of freedom, independence and peace, but it happens to be a concept that America's European allies can embrace wholeheartedly. After all, the French have Joan of Arc — later beatified as Saint Joan for her efforts to restore peace and freedom. For three centuries, Britain has had leaders and liberators from Cromwell to Churchill.

Frankly, most of Europe -- or indeed much of the rest of the world, including the Middle East, North Korea and China, not to mention Vladimir Putin's Russia -- never paid much respect to President Obama's embrace of that doctrine, since he was only too rarely prepared to back it up with action or enforcement.

Effectively, Obama carried out half of John Quincy Adams' statement or Woodrow Wilson's 14 Points. He supplied the moral imperative but failed to follow through with a concrete directive.

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After President Obama drew his vaunted " red line " over the use of chemical weapons by Syria's Bashar al-Assad, a vitriolic debate in Britain's House of Commons led to England backing out of any joint action. Obama wimped out, which incidentally left the French, who'd been prepared to back him, hanging out to dry.

Indeed, his two secretaries of state, Hillary Clinton and then John Kerry, often tried to get Obama to take actions they could use as a negotiating wedge -- whether with Syria, China and its islands in the South China Sea, North Korean and its nuclear weapons or Russia and its incursions into eastern Ukraine.

In fact, President Trump's cruise missile strike at the Syrian airfield was more of an object lesson -- a demonstration of what the United States can do and proof that he is prepared to deliver on the kind of credible threat that Obama only postulated.

It remains to be seen whether this one-shot demonstration of force will have a transformative effect in other theaters where there are threats to our own security and the tranquility of the world.

Will Kim Jong Un hesitate before firing off his next nuclear test or a long-range missile? Will China slow its expansion into the South China Sea? Russia has already suggested it will not be turned from its alliance with Assad and sent a frigate to its naval base on the Syrian coast to prove it. But what about further adventures in eastern Ukraine or the Baltics?

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The biggest question is whether Trump, having proven his willingness to stand and fight and not cut and run, will find others prepared to follow him. Considering how perniciously some world leaders and even members of his party have been treated by him to date, it could take some time to get that support.

In any event, as John Quincy Adams concluded, "once enlisting under other banners than her own ... the fundamental maxims of [America's] policy would insensibly change from liberty to force."

That change, it would appear, has already begun. If it persists and becomes embedded as a Trump Doctrine, only then can its impact be truly assessed.