Keith Johnson writes:  During a four-hour helicopter ride over the Black Sea and the Sea of Marmara in early February, Turkish Energy Minister Taner Yildiz and Russia’s Gazprom boss, Alexey Miller, mapped out plans that could potentially rebuild the long-adversarial relationship between their two countries.

But Yildiz and Miller also traced what could be the newest fault line in Europe’s geopolitical landscape. That helicopter ride, and the subsequent formal agreement signed in early May, suggest Turkey’s patience with Brussels is wearing thin—the EU, after all, has been slow-footing the country’s membership for decades now—and Ankara’s willingness to support Europe’s foreign-policy priorities, from diversifying energy resources to isolating Russia, is diminishing. Now, this one pipeline, which could deliver gas as early as next year, could have the power to embolden Russian President Vladimir Putin, endanger a critical alliance the West has spent decades cultivating, and upend Eurasia’s entire energy and security landscape.

Turkey would become a middleman for Europe’s energy buyers, and it would be precisely the linchpin Moscow needs to keep an energy hold on the continent.   Turkey Plays the Gas Game