Jessica Durando

USA TODAY

Turkey held a constitutional referendum Sunday that would radically change President Recep Tayyip Erdogan country's system of government and give the president vast, new powers.

So, why does that matter to the United States? Here are three major reasons:

Secular democracy at stake

Opponents campaigning against the referendum say Erdogan would undermine Turkey's democracy and secular traditions and institute a religious authoritarian regime in the mostly Muslim nation, which provides a bridge between Europe and its Western values and the Middle East.

Political critics point to the government crackdown following an attempted military coup last July and pressure for women to cover up in Muslim clothing.

A more powerful Erdogan, who could be around at least another decade, worries Western leaders who have expressed concerns about his move away from democracy. That has made the European Union less receptive to Turkey's bid to become a member.

U.S. air base

The U.S. military has a vital air base in Turkey that is used for operations throughout the Middle East.

U.S. Air Force Col. John Dorrian said in January that any actions by Turkey to shut down or limit U.S. air operations out of Incirlik Air Base would be damaging for the U.S. campaign against the Islamic State —also known as ISIS — in Syria.

"It's absolutely invaluable ... for the coalition," he said. "The entire world has been made safer by the operations that have been conducted there. It's a very important base to the coalition and to the ongoing fight against (ISIS)."

Strategic U.S. ally

The NATO member is a valued ally in the fight against ISIS and the defense of Europe. In addition, Turkey is trying to keep the tide of refugees fleeing Syria and other conflict zones from flooding Europe.

Turkey has the second largest army in NATO and is key to any success in rolling back and eventually defeating ISIS in Syria and Iraq.

President Trump has spoken about the two countries' "shared commitment to combating terrorism in all its forms" and has welcomed Turkish contributions to the fight against ISIS. On Tuesday, the White House said Trump called Erdogan to "congratulate him on his recent referendum victory" and to discuss the recent U.S. action in response to the Syrian regime’s use of chemical weapons."

Both leaders, according to the White House, agreed on the importance of holding Syrian President Bashar Assad accountable and discussed cooperation efforts to combat terror efforts.

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