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LONDON - U.S. Vice President Joe Biden began a reassurance tour of east European allies Tuesday, promising that the current diplomatic crisis over Russia would leave NATO “stronger and more unified than ever.”

But some experts say the showdown over Ukraine has exposed the organization as toothless in the face of Vladimir Putin’s triumphant annexation of Crimea.

While Biden was in Warsaw promising to “stand shoulder to shoulder” with Poland, Putin was making a defiant, barnstorming speech at the Kremlin that placed new pressure on the United States to act.

Ukraine is not a member of NATO, despite many years of speculation that it is poised to join, and therefore it is not automatically protected under Article 5 of the North Atlantic Treaty – the clause which regards any attack on one member state as an attack on all.

“That’s going to make it very difficult for NATO to do anything of significance,” said Andrew C. Kuchins, a senior fellow and director of the Russia and Eurasia Program at the Center for Strategic and International Studies, a Washington, D.C.-based think tank. “It’s more likely that any action will be taken by a coalition of the willing.”

Does that mean NATO is essentially toothless? “Yes, I think it does,” said Kuchins.

Sanctions dismissed as 'pathetic'

With NATO currently powerless to stage a military intervention over Crimea, its members have instead turned to visa and economic sanctions on Moscow – a response that a veteran British ex-foreign minister dismissed Tuesday as “pathetic.”

“All the international community has done so far is implement visa sanctions and asset [sanctions] ... That is a pathetic response.”

“This is the most dangerous crisis we have faced, and it's a crisis for Europe not just Ukraine,” Malcolm Rifkind said in a BBC radio interview, describing the lack of consensus for military action as “very disturbing.”

“All the international community has done so far is implement visa sanctions and asset [sanctions]," Rifkind said. “That is a pathetic response.”

Are sanctions enough to force Putin to reconsider? Only if they cause Russia to become economically isolated, according to Robert E. Hunter, a former U.S. Ambassador to NATO and a member of the board of directors at the European Institute.

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“[Sanctions] will have no immediate impact – economic sanctions never do,” Hunter wrote on the Institute’s web site, but they could erode the trust that Russia needs in order to have productive economic relations.

“This is not the Soviet era, when Russia [then the Soviet Union] could turn its back on the outside world and pursue autarky. It has to be engaged in the outside world, economically, or its economy will stutter and then, despite all of the patriotic support for Putin now, he will be in big trouble politically at home.”

Expect a military show of force

NATO does have some military options, including the deployment of its 14,000-strong response force, but that would require the agreement of all 28 member states and there is a notable lack of appetite for combat in a region that has witnessed much conflict in recent decades. The last major NATO-led intervention in Europe was in Kosovo in 1999.

“After ten to 12 years of military intervention in Afghanistan and Iraq, there is a feeling that the use of force isn’t necessarily the best way to resolve conflict,” said Kathleen McInnis, research consultant on NATO at London-based think tank, Chatham House. “We have seen that reluctance to intervene recently in Syria and in Libya.”

NATO also balked at taking on Russia in 2008 when Moscow invaded Georgia. Like Ukraine, Georgia had been wooed by NATO but never formally adopted as a member, and NATO declined to intervene.

German Chancellor Angela Merkel ruled out military action over Ukraine in a speech last week that reaffirmed the European Union ideal of collectively-enforced peace.

So what can NATO do to emphasize its military strength? Expect a ramp-up of military assets and training exercises right along NATO’s eastern frontier, according to McInnis.

Such is the fear of Moscow in eastern Europe and the Baltic states that some members along the Russia border want NATO to send in ground troops.

"Increased presence of NATO allies in our region would make sense, both militarily as well as serving as a deterrent," Estonian Defense Minister Urmas Reinsalu said as military surveillance aircraft took flight over the region. "Living next door to the Big Bear means that we need a solid defense platform."

At Warsaw's request, the U.S. last week sent some 300 air troops and a dozen F-16 fighters to Poland for joint training in a show of military support.

Standing next to Poland’s Prime Minister Donald Tusk in Warsaw, Biden said Tuesday that the U.S. had also increased the number of U.S. jets involved in air patrols over Estonia, Latvia and Lithuania. “Instead of 4 F-15s we have sent 10,” Biden said.

A chance to reinvigorate NATO?

On Wednesday, the Vice President will continue his regional tour with a meeting in Vilnius with Lithuanian President Dalia Grybauskaite and Latvian President Andris Berzins.

“Recent events remind us that the bedrock of our alliance remains collective self-defense as enshrined in Article 5 of the NATO treaty,” Biden said. “We take it deadly seriously and our commitment is absolutely unwavering and unshakeable.”

That leads some to believe that the Ukraine crisis could reinvigorate NATO, dragging the 65-year-old organization out of a torpor induced by the grinding U.S.-led campaign in Afghanistan.

The Crimea crisis "is providential from the point of view of NATO," Nick Witney of the European Council on Foreign Relations told The Associated Press. "It gives it a new lease on life."

But while NATO members enjoy reinforced military might, Ukraine could be forgiven for feeling a little raw over the Budapest Memorandum – a 1994 agreement signed by the U.S., Russia and Ukraine in which Kiev gave all its ex-Soviet nuclear arsenal to Russia in exchange for a commitment to protect its borders.

“That agreement is looking pretty worthless right now,” said Kuchins. “If I was a Ukrainian, I think I would be asking for my nukes back.”

NBC News’ Abigail Williams in Washington D.C. and The Associated Press contributed to this report.