WARSAW -- The dominant vibe in Warsaw is all about unity. The results are mostly pre-cooked. And there should be few surprises.
With little dissent to speak of, in the next couple days NATO is expected to beef up its forces in its vulnerable front-line states in the east; forge closer ties with traditionally neutral Finland and Sweden; and upgrade the importance of cyberdefense.
"I hope that we are going to prove that the transatlantic alliance is in better shape than ever before," Polish President Andrzej Duda said.
But lingering tensions lurk below the surface at a summit NATO officials describe as the most consequential since the end of the Cold War.
The centrifugal forces tugging at the European Union are also threatening to strain the transatlantic alliance.
The traditional differences among member states about how forcefully to confront Moscow, however latent at the moment, can easily become manifest again.
A split is emerging between NATO members who see the greatest threat to the alliance coming from the east, from a revanchist Russia, and those who would prioritize the danger from the south, from radical Islam.
And with populism on the rise across the West, NATO faces "stiff political headwinds," former U.S. Secretary of State Madeleine Albright noted in her keynote address to the Warsaw Summit Experts' Forum, a conference on the sidelines of the summit.
"On both sides of the Atlantic, there are myopic voices questioning NATO's purpose," Albright said.
So, what are these stiff headwinds? And what are some of the underlying issues dividing the alliance?
The Specter Of Brexit
The elephant in the room, of course, is the United Kingdom's vote last month to leave the European Union and fears that this could have a knock-on effect with NATO.
The official line is that it won't.
"Brexit will change the U.K.'s relationship with the European Union, but it will not change the U.K.'s leading role in NATO," alliance Secretary-General Jens Stoltenberg told the Warsaw Summit Experts' Forum.
But not everybody was convinced.
James Sherr of Chatham House noted that the Brexit vote "could weaken the transatlantic impulse" in the EU.
Polish President Duda suggested the effect Brexit could have on the U.K. itself, including the possible fracturing of the country, could automatically change Britain's role in NATO and weaken the alliance.
And others stressed that the populist and nativist forces that drove the Brexit debate -- and were cheered on by the Kremlin -- could also work to undermine NATO.
Underlying all this is a fear that Brexit wasn't a localized British phenomenon but a global trend against multilateralism.
"We need to return to a transatlantic conversation about the health of our democracies," Heather Conley of the Center for Strategic and International Studies said.
Likewise, Albright said bluntly that "NATO leaders have no choice. They must do a better job of building domestic support."
The Language Of Bucharest
Meanwhile, 11 words in an eight-year-old declaration continue to haunt and divide NATO.
A pledge made at one of NATO's most contentious summits, in Bucharest in April 2008, caused something of a minor dust-up in the run-up to this week's landmark gathering in Warsaw.
Point 23 of the alliance's 2008 Bucharest Declaration began as follows: "NATO welcomes Ukraine’s and Georgia’s Euro-Atlantic aspirations for membership in NATO."
And then came those 11 words: "We agreed today that these countries will become members of NATO."
That pledge was the result of a frantically negotiated political compromise.
The 2008 NATO summit in the Romanian capital was hopelessly divided over whether to give Georgia and Ukraine Membership Action Plans, final blueprints for joining the alliance, which Russia hotly opposed.
The United States, United Kingdom, Poland, and the Baltic states were in favor. Germany, France, and Italy were against.
Unable to achieve unanimity, the alliance was forced to hand Georgia and Ukraine a consolation prize -- and the "Bucharest language" has been reaffirmed at every summit since.
But in the weeks preceding the Warsaw summit, the same divisions that caused the schism in Bucharest reemerged with some members pushing for the language not to be reaffirmed.
In the end, NATO officials say a decision was reached to reaffirm the Bucharest language explicitly for Georgia and implicitly for Ukraine.
But the very existence of such a debate illustrates that the issue of how closely to engage aspirants like Georgia and Ukraine continues to be deeply divisive.
Permanent And Substantial
Likewise, there are divisions among member states -- and within member states -- about how forcefully to confront Russia.
German Foreign Minister Frank-Walter Steinmeier recently called NATO exercises in Eastern Europe "saber rattling" -- appearing to oppose the policy of Chancellor Angela Merkel's government.
And some southern European states, like Italy and Greece, would prefer to see NATO focus less on Russia and more on the threat emerging from instability in the Middle East and North Africa.
"We don't have the luxury of a choice," Albright told the Warsaw Summit Experts' Forum, stressing that the alliance must focus on both threats.
Additionally, in a decision that is proving controversial, the NATO-Russia Council -- which was suspended following the annexation of Crimea -- is scheduled to meet following the Warsaw summit.
Stoltenberg defended the decision in Warsaw, saying that the council was designed to be an "all-weather forum for dialogue."
And despite the buildup on its eastern flank, the alliance is still trying to adhere to the NATO Founding Act, a 1997 agreement with Moscow to assuage the Kremlin's fears about former Warsaw Pact members Poland, Hungary, and the Czech Republic joining NATO.
In the Founding Act, NATO pledged that it would not station “permanent” or “substantial” forces on the territory of its new eastern members.
Permanent and substantial, however, were never defined in the Founding Act, which alliance officials say is a "political" and not a "legal" document.
The Baltic states, Poland, and Romania have long argued that Russia has breached its obligations under the Founding Act. They sought at the alliance's last summit in Wales to deemphasize -- and possibly revoke -- the pledge.
But the alliance opted instead to take advantage of the elasticity in the terms "permanent" and "substantial."
As a result, the troops in the Baltics, Poland, and Romania will technically be a mobile force on rotation, using warehoused equipment, and backed by NATO's 40,000-strong rapid reaction unit.
But the debate over "permanent and substantial" is far from over.
In a speech in May, Estonian President Toomas Hendrik Ilves noted that in the Founding Act, the pledge was explicitly predicated on the security environment in 1997 -- with a relatively benevolent Russia -- remaining the same.
But that environment, Ilves said, "has changed beyond recognition."
In a recent interview with Deutsche Welle, Estonian Prime MInister Taavi Roivas said regardless of whether the troops are called permanent or not, "they must be constantly present. There cannot be any gaps. Deterrence has to be the new normal."
The lingering divisions in NATO should not be surprising.
"Everything we do is defensive, transparent, and consistent with our international obligations," Stoltenberg said.
And getting 28 democratically elected leaders to agree on anything -- let alone the thorny issues facing NATO -- is going to be a challenge.