It sounds dramatic but the upcoming heads of government meeting in London this December makes remedying the Alliance’s long-standing flaws a matter of existential urgency.

The best news is the most obvious—the accession of Northern Macedonia, following the resolution of the shamefully protracted dispute with Greece about the former Yugoslav republic’s name. This rare note of good news in the Western Balkans is a snub to Kremlin attempts to stoke extremism and sow mischief in this fragile region. But success on that front highlights failure on another, in dealing with two candidates more critical to the Alliance’s mission, Georgia and Ukraine. By freezing their membership applications indefinitely the Alliance has all but accepted a Russian veto on its future enlargement. NATO needs to find an answer on this by December.

Another bit of good news is that the Alliance is now back in business in its core mission of territorial defense. Following decisions at the summit in 2016, it has multinational trip-wire forces in Estonia, Latvia, Lithuania, and Poland and is developing a tailored presence in the Black Sea. Plenty to celebrate: real troops, real plans, and real exercises in the countries most vulnerable to Russia make war less likely, not more.

But there are still gaping holes in NATO’s strategic concept. One question is about decision-making in a crisis. Does General Curtis Scaparrotti, the Supreme Allied Commander Europe (SACEUR) and the senior American general on the continent, have the authority to move forces to the frontline as he sees fit? Or must he wait on the Alliance’s decision-making, which is slow and at risk of political obstruction from countries where Kremlin influence operations have bitten deep.

Another question is what happens if the trip-wire is tripped? The Alliance has made progress here, with the Very High Readiness Joint Taskforce (VJTF), an 8,000-strong expeditionary force certified in the Trident Juncture exercise last year. This year Germany is providing the VJTF’s backbone.

But beyond this spearhead force, NATO’s capabilities are worryingly weak. Bringing heavy reinforcements from the United States to Europe will take many weeks. That highlights the weakness in the nuclear deterrent. Russia is investing heavily in new battlefield (“tactical”) nuclear weapons. It rehearses their deployment and use in its war games. NATO has only a few of these in Europe, almost all in U.S. hands. Public opinion is hostile to them, in some countries extremely so. Deterrence depends increasingly on the least credible end of the nuclear spectrum, the strategic (doomsday) arsenal. NATO needs to talk about nuclear posture, and the conversation will not be easy.

But perhaps the most difficult questions of all for the summit are not military, but political. The paradox of the U.S. security relationship with Europe is that while the facts on the ground have never been more encouraging, the mood in the air has never been bleaker. NATO only narrowly escaped disaster at its summit last summer, when according to some observers, President Donald Trump seemed ready to announce a U.S. withdrawal from the Alliance. At that meeting the U.S. leader demanded that allies spend 4% of GDP on defense – an unattainable goal. Though European allies are increasing their defense budgets, the row over spending is likely to resurface, perhaps in spectacularly damaging form. The danger is not that the United States abandons Europe altogether, but that the focus shifts to bilateral relationships with the United States, creating a competition for influence that weakens alliance cohesion.

All these problems are solvable, but they require energetic, focused political leadership. Looking around Europe’s weak governments, crowded electoral calendar, and self-imposed distractions, it is hard to see where that is coming from.