A new American deal for Europe

Editor's note: This commentary originally appeared in The Wall Street Journal.

Britain's decision to leave the European Union opens an era of political disruption, but along with it comes opportunity. The U.S. can seize this moment of uncertainty to reassert its leadership of a Western alliance of free nations.

Britain and Europe are masters of their own fate, but the Continent has always benefited when a confident America points in the right direction. The Obama era has been marked by U.S. indifference and de facto default to the EU, the kind of supranational body President Obama thinks should rule the world.

But the EU has proved unequal to the urgent tasks of reviving economic growth and resisting security threats on its eastern and southern borders. It's time for the U.S. to get back in the game because America needs a confident, prosperous Europe as a partner to defend the West against the rise of authoritarian regimes and global disorder.

An important first signal would be for the U.S. to invite the U.K. to begin bilateral free-trade talks that run alongside current talks with the EU. Mr. Obama may not be able to rise above his pre-Brexit taunt that Britain will move to "the back of the queue" on trade. But this would not be his first strategic mistake.

A trade deal with the world's fifth-largest economy -- and one of Europe's healthiest -- is in America's interests for its own sake. A two-track trade negotiation would also help the British in their negotiation over new terms of trade with the European Union by giving Britain the leverage of a U.S. alternative. U.S.-British talks could also prod Brussels to move faster and rebuff the French protectionism that is infecting the EU-U.S. talks.

Whether or not Mr. Obama leads, Hillary Clinton and Donald Trump should. Republicans in particular have a great opportunity to shore up a crucial alliance. Mr. Trump and House Speaker Paul Ryan can take the advice of our friends at the New York Sun and hold a joint press conference saying they'd welcome British trade talks. This would show statesmanship by Mr. Trump, allay some of the concerns about his protectionism, and offer a welcome opportunity for the two men to agree about something.

Mr. Trump says he's not against trade, only against bad trade deals. Here is a moment to show he means it. He could also say he will meet with the new British Prime Minister as soon as possible if he is elected, and that America's relationship with the U.K. is as important as any in the world.

Brexit also creates an opening to reinvigorate NATO. The transatlantic defense alliance has always been broader and sturdier than the European Union in providing European security, and now it will be the main vehicle for British influence in Europe. This can be a healthy development, especially if it frees Europe from a distracting and generally quixotic attempt to create an EU security structure that overlaps with NATO.

A stronger NATO is essential as Vladimir Putin accelerates his divide-and-conquer strategy in the wake of Brexit. NATO's decision this month to deploy four new battalions to Poland and the Baltics is a start, but the Russians will continue to press for weaknesses and to persuade Germany to cede Ukraine as part of Russia's political and economic orbit. The next U.S. president should shore up Western unity by committing more U.S. resources and sending lethal defensive weapons to Ukraine.

Better security for a realigning Europe also requires a more coherent energy policy. After too many years of debate, Washington has finally allowed exports of natural gas that can help break Russia's stranglehold on Europe's energy markets. The next president should make it easier to develop and export U.S. energy to Europe.

The Brexit vote has produced a weekend of handwringing, especially from progressives who find democratic uprisings too messy for their tastes. But now that it has happened, the goal should be to seize this moment for reform and rejuvenation. The U.S. can help by reasserting the commitment to Europe it has too often abandoned during the last eight years.