More broadly, for the European Union and Washington there is the strong feeling that Turkey under Mr. Erdogan has moved farther away from European values and norms like the rule of law and freedom of the press.

Kaja Kallas, Estonia’s prime minister, said in an interview that NATO and the European Union viewed the election differently. It is a defense alliance, she said, and “Turkey is one of the allies that has great military capacities” to help NATO in a key part of the world. “So I don’t think anything changes in terms of NATO in this regard whoever wins the elections.”

For NATO, of course, the hope is that a change of leadership in Turkey will end the standoff over approval of Sweden’s membership in the military alliance, ideally before a summit in Vilnius, Lithuania, in July.

In Washington, Mr. Erdogan’s drift toward authoritarianism, his ties to President Vladimir V. Putin of Russia and his disputes with NATO have exasperated officials — and even led some members of Congress to suggest that Turkey should be banished from the NATO alliance.

While the United States, the European Union and, to a lesser extent, NATO stand to gain from an opposition victory, Mr. Putin almost certainly will be seen as the loser if Mr. Erdogan is ousted.