John Avlon is a CNN political analyst and anchor. The opinions expressed in this commentary are his own. View more opinion articles on CNN.

(CNN) Since the Second World War -- spanning 14 US presidents, Republican and Democratic -- the occupant of the Oval Office has been referred to as "the leader of the free world." Until now.

Over his 18 months in office, Trump has surrendered that mantle without a mandate to do so. Trump's impulse is to echo Russian President Vladimir Putin's talking points and advance his agenda, even as elements of his administration attempt to push back to protect longstanding American interests.

Time and again the world has witnessed what journalist Luke Harding describes in his book "Collusion" as Trump's "weirdly deferential behavior toward Putin -- his singular reluctance to criticize, his boundless willingness to appease, his desire for face time."

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This past week offered new lows in this shameful dance on the world stage, capped by what Anderson Cooper diagnosed as a "disgraceful" performance at Helsinki, in which Trump was more critical of Democrats and his own Justice Department than of Putin or Russia.

In the days before his largely unsupervised chat with Putin in Helsinki, Trump attacked our NATO allies at a Belgian summit, suggesting the US could "go our own way." He nonsensically blamed President Barack Obama for Russia's invasion of Crimea, insulted German Chancellor Angela Merkel, undercut embattled British Prime Minister Theresa May over Brexit and described the European Union as a "foe" of the United States.

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