Dan Janison Melville. N.Y. Tuesday January 26, 2010. Daniel Janison,

Dan Janison has been a columnist at Newsday since 2007.

Maybe the virtues of discreet diplomacy are overstated after all.

Or maybe a volatile change is under way in U.S. foreign relations, with unpredictable results.

President Donald Trump on Tuesday claimed credit for Qatar’s new isolation on the Persian Gulf, suggesting it came out of his anti-terrorism appeal on a recent Mideast trip.

Bahrain, Egypt, Saudi Arabia, the United Arab Emirates and Yemen have cut off relations with Qatar.

Qatar has long been accused of funneling arms to radical groups elsewhere. (The same has been said of Saudi Arabia.)

Trump’s exact role in this move — beyond tweeting about it — had yet to be corroborated Tuesday.

A similar Qatar cutoff by most of the same nations was resolved in 2014.

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There have been stories in recent weeks that the other heads of state were miffed about Qatari relations with Hamas or Israel or Iran, or a recent deal to release wealthy hostages taken during a hunting trip in Iraq.

Perhaps it was a mix of those.

The implications for the U.S. and Trump going forward are military and economic.

If Trump’s claims sound a little surprising, it may be because of what he said no further back than May 21.

That day the president told the Qatari emir, Tamim bin Hamad al Thani: “One of the things that we will discuss is the purchase of lots of beautiful military equipment because nobody makes it like the United States.

“And for us, that means jobs, and it also means, frankly, great security back here, which we want.”

More important, Qatar hosts a sprawling and important U.S. air base relevant to past and future American operations in Iraq, Syria, Afghanistan and other countries in the region.

Also, Trump has had his share of business in the now-shunned country. Before he took office in January, Time magazine reported on his stakes in four companies “that appear to be tied into business in the desert nation.”

Qatar Airways has leased space in Manhattan’s Trump Tower since 2008. And Ivanka Trump told a trade magazine two years ago that the Trump Hotel Collection was looking at opportunities in Qatar.

The bottom line is that nobody knows how Trump’s boast-of-the-day will affect the air base or American commercial interests or relations with other nations or the bigger power rivalry between Saudi Arabia and Iran.

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Trump’s Qatar blurt eclipsed another in recent days in which he attacked London Mayor Sadiq Khan, with whom he’s had issues before, for advising against public alarm about heightened police presence in the wake of the latest terrorist attacks.

Now there is debate over Trump’s planned trip to the United Kingdom.

The key question is whether presidential verbal snipes have a practical impact on U.S. interests — or just provide idle tabloid and TV fodder of little consequence.

As with the Justice Department’s defense of Trump executive orders or Russian embroilments, there are undoubtedly people in his government and other governments trying to just work around whatever message he last sent out.