The British or, to be more accurate, the English and the Welsh have voted to leave the European Union by a convincing margin. This will be a difficult transition for Britain; divorces are usually much more expensive and more bitter than either side expects at the beginning, and hammering out new trade and banking rules to govern Britain’s relations with its jilted neighbors is going to be tough.

David Cameron made three good decisions in the wake of the vote. He is right to step down, right not to do it immediately and right to leave the task of beginning the formal secession procedures to his successor. Both financial markets and British politics need some time to adjust to the new realities and a period of informal consultations and negotiations before the formal process begins makes sense.

For Americans, the British decision is a bitter blow. NATO, the European Union, Great Britain, Germany and the West generally are all in a worse position now than they were before the vote. Not only will Western institutions be turning inward to deal with the consequences of British withdrawal, the balance of power inside the EU will shift away from the outward looking and dynamic north towards the more protectionist south. Even as the global situation deteriorates and the Middle East lurches deeper into the horrors of sectarian war, America’s close European allies will be squabbling with each other over the details of divorce—and both the EU and Britain will be consumed by their internal problems. Scotland may now want to leave Britain, and populist politicians across Europe are already talking about more secessions and more referendums.

The vote, and weakening of the West that it heralds, will diminish President Obama’s foreign policy legacy. American policy toward Europe under his leadership has been an abject failure. His most obvious failure, and one that historians will view severely, is his failure to prevent the meltdown of Syria. The millions of desperate refugees fleeing for their lives are much more than a humanitarian disaster; they are a political disaster, and the strain of coping with the refugee flow on top of Europe’s other problems stoked suspicion and fear across the continent and greatly strengthened the power of the Leave campaign in the UK.

But beyond the horrors of Syria, Obama has done less for Europe than any American president since the 1930s. The American response to the euro crisis and its long and bitter aftermath was both shortsighted and feeble. To the extent it did anything, the Obama irritated the Germans by critiquing their handling of the crisis while disappointing the debtor countries by an absence of effective support. The United States had great interests at stake when it came to Cameron’s negotiations with the EU; from all one can tell, President Obama spent more time playing golf during those negotiations than he did working to prevent a damaging split between some of our most important partners and allies. Smart American diplomacy would have worked intensely and unremittingly to get a deal between London and its partners that the British people would support, but despite the President’s breathtaking self-confidence, smart diplomacy is not actually part of his skill set.

One hopes that even at this late date the Obama Administration will realize that the future of the UK-EU association is of almost infinitely greater importance to American national interests than launching yet another poorly conceived peace offensive in the Middle East. American diplomats and Treasury officials need to be working hard to generate ways to minimize the damage of this decision to the West.

The British people have the right to choose whether or not to remain in the European Union, and while there will be some in Europe who want to punish them for this choice, the American interest in this matter is clear. We want a strong Britain, a strong Europe, good relations on both sides of the Channel and a trading system that doesn’t put new bureaucratic obstacles in the path of American exports or investment. We do not want bitterness and friction over the break to throw sand in the gears of western political and security cooperation in an increasingly dangerous world. We do not want Europe’s divisions to become Putin’s opportunities. We want Europe to be united, and we want Britain to be Great.

At the same time, the U.S. government needs to do something else that the current administration has unaccountably failed to do over the last seven years: develop a strategy to help save the EU. The European Union is in trouble; the world’s most audacious experiment in international relations is looking both fragile and sclerotic. The British aren’t the only Europeans who think Brussels is a disaster, and the chance that a post-Brexit EU will continue to weaken and fragment is dangerously high. Refugee flows from the Middle East and North Africa are bound to continue. There are few signs of real economic revival in the south. The torpid bureaucracies and dysfunctional political organizations of Brussels can’t deliver real solutions to Europe’s problems, but European nation states have given so many of their powers to the EU that in many cases they lack the ability to act when Brussels fails.

From the 1920s to the present day, American engagement in Europe has been a necessary though not a sufficient condition for European success. And when the Americans walk away, Europe tends to fail. The Americans walked away during the Bush and Obama years, and the consequences of that withdrawal are becoming apparent. If we had engaged earlier and more effectively, Brexit might never have happened. Now that it has, a thoughtful and serious American re-engagement with our friends and allies in Europe is more important than ever.