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If there has been any constant in the Republican worldview over decades, it's that American strength, resolve and credibility are essential in foreign affairs, and weakness and uncertainty lead straight to disaster. The GOP legions regard Barack Obama and Hillary Clinton as failures because they have been insufficiently willing to challenge our adversaries and stand with our friends.

"Our allies don't trust us, and our enemies don't fear us" is a claim made by one Republican after another. But the Cleveland convention was a study in dissonance between the bedrock convictions of just about every loyal Republican and the opinions of the presidential nominee.

People who denounce Obama for "leading from behind," appeasing Vladimir Putin, failing to go to war against Bashar Assad and criticizing America lined up in support of Donald Trump -- whose policies are subject to exactly the same criticisms. There is much to fault in the GOP's past approach, but Republicans are in a strange position: They unquestionably affirm their long-standing policies without seeming to realize their candidate doesn't.

Retired Lt. Gen. Michael Flynn proclaimed to the delegates, "There is no substitute for American leadership and exceptionalism." Trump, however, affects nonchalance on such matters.

Exceptionalism? "I don't know that we have a right to lecture (other countries)," Trump said in an interview with The New York Times. "How are we going to lecture when people are shooting our policemen in cold blood?" Imagine what Chris Christie would say if those words had come out of Obama's mouth.

How about leadership? Trump indicated it's no sure thing that we'd honor our treaty obligation to defend any NATO member attacked by, say, Russia. "If we cannot be properly reimbursed for the tremendous cost of our military protecting other countries," he said, "I would be absolutely prepared to tell those countries, 'Congratulations, you will be defending yourself.'"

Hmm. It's almost as though under President Trump our allies wouldn't be able to trust us. Asked about the value of our presence in South Korea, which has coincided with 60 years of peace, he scoffed. Without it, he speculated, "maybe you would have had a unified Korea."

Japan? "Well, what are we getting out of this?" All of these allies, he suggested, should never be completely sure of our commitments. "In a deal, you always have to be prepared to walk," he explained.

Compare Trump's comments about NATO with Ronald Reagan's in 1988: "We often say that if the bomb is dropped in Amsterdam, it is the equivalent of dropping a bomb on Chicago." Reagan would have said the same about Seoul and Tokyo. Trump apparently thinks a bomb dropped on Amsterdam is a bomb dropped on Amsterdam, nothing more.

What about making sure our enemies fear us? Christie excoriated Clinton for once expressing hope that Assad would be better than his father, who preceded him as ruler of Syria. Trump, however, is not itching to go after the regime. "I think that ISIS is a threat that's much more important for us right now than Assad," he said.

Russia? "I think Putin and I will get along very well," he said. "It would be wonderful if we had good relationships with Russia so that we don't have to go through all of the drama."

Republicans have denounced Obama for denying lethal defensive military aid to Ukraine after its invasion by Russia. But Trump blocked an endorsement of such help in the platform -- which pledges only "appropriate assistance." Do the delegates think that will make the Kremlin quake in fear?

The GOP standard-bearer manages to distract attention from these violations of Republican security orthodoxy with his ostentatiously macho talk -- about bombing the Islamic State and vowing that Iran will "never, ever be allowed to have" nuclear weapons. But behind the rhetoric are ignorance and confusion.

Never has the GOP nominated someone whose intentions are so unpredictable. The conservative principles for ensuring our security and spreading our values have been turned over to someone who doesn't seem to understand them, much less champion them. In effect, he has emasculated the party's foreign policy.

In his acceptance speech, Trump drew lusty cheers as he blamed Clinton for all the trouble in the world. The stark irony is that if anyone in the race is likely to uphold the traditional Republican strategy, it's Clinton.

The delegates, like our enemies and allies, have no real idea how President Trump would operate in a perilous world. The difference is that our enemies and allies actually give a damn.