Donald Trump is heading to NATO's summit in Ankara, and European leaders are holding their breath.

The president will touch down in Turkey on Tuesday following a grueling week of Independence Day festivities and public relations setbacks, involving his disastrous Great American State Fair. He'll meet with Turkish President Recep Tayyip Erdogan before joining other alliance leaders for dinner.

According to a report from the Washington Post, Trump has already made his lack of enthusiasm obvious before even departing. He told NATO Secretary General Mark Rutte he wouldn't bother attending at all if Erdogan weren't hosting. When pressed on what he expects from NATO members, his answer was stripped of diplomatic niceties: "I just want loyalty."

The president has spent recent days hammering the alliance on social media, asserting that America bankrolls the entire operation while gaining nothing in return. "The United States spends more money on NATO than any other country, by far, to protect them, without getting any benefit from so doing," he posted.

According to the Post, "One senior European diplomat fretted that Trump would arrive in Turkey exhausted and angry after a week of tiring travel, including a 3:30 a.m. Saturday return from an event at Mount Rushmore and a rally on the National Mall later that day in the sweltering Washington heat."

That volatile emotional state could prove consequential. "Europeans are nervous that the way [Trump] feels about NATO is that this is not fundamentally in U.S. interests," Max Bergmann of the Center for Strategic and International Studies told the Post. "Especially now as there's more domestic political pressure on European leaders to be seen as standing up to Trump."