Horror.  Sadness. Shock. And then fear.

This was the procession of sentiments coming from Afghan-Americans who watched this week as a killer and terrorist who murdered 49 people turned out to be one of their own.

 “This is a tragedy. And no one can believe it,” said one friend whose family fled southern Afghanistan when the Russians invaded and found safety in America in the 1980s.

But in this moment of grief is also a shiver of fear that a country to which they belong is now turning its sights on them and those who share their faith. And in this moment of terror is a time to define who we are as Americans.  

Do we believe that blocking all members of a world religion would keep us safer? Do we speak seriously about a blanket “ban” on members of a faith whose sons and daughters serve in and out of uniform at war? Are we prepared to keep out of this country Afghan and Iraqi Muslims who risked their lives each day to be the eyes and ears and voice of U.S. soldiers on the battlefield?

So far, the answer is no. As Gallup noted at the end of last year, “a majority of all groups” say Muslims are “loyal to the U.S.”

Gallup also found that “a majority of all religious groups in the U.S. disagree with the statement that ‘Muslims living in this country are sympathetic to Al Qaeda.’”

In fact American Muslims have served their country in what George W. Bush called the War on Terror these past fifteen years. And when America said to its citizens of Afghan heritage back in 2001 that it needed their help on the battlefield, there was no “them.” Only us.

I spoke recently with an interpreter who served America at war in Afghanistan. No one in her family wanted her to go back to a country they had risked their lives to flee. But she went back anyway because she thought her country, America, needed her and she wanted to make a difference.

In 2011, she nearly lost her life for her country while on a special operations night raid targeting terrorists in Afghanistan. She still has not recovered from the surgeries she needs to use her arm again.

What does it say that she now fears for her mother’s safety when her mother goes to her local mosque to pray during the holy month of Ramadan? That she tells her mother not to wear her head scarf because she notices the dirty looks she has been getting when they are out in public.

Is it not enough to nearly lose your life on the battlefield to prove you are American? Now you have to lose your faith?

This is not about Muslims as a group; this is about us as a nation.  And who we are as the United States of America, indivisible, with liberty and justice for all – not just for some depending on their religion.

 “Our nation is a nation of immigrants. More than any other country, our strength comes from our own immigrant heritage and our capacity to welcome those from other lands.” These words belonged to President Ronald Reagan. In 1981.

Afghan-Americans have served this country since the start of the war in and out of uniform. They have contributed as translators, development experts, local eyes and ears and advisers.

Former First Lady Laura Bush continues to lead the Afghan Women’s Council out of Georgetown University and just published a book on the courage and grit of Afghan women, some of whom have found new lives in America.

Afghans and Iraqis who risked their lives alongside American forces face death threats at home and Sen. John McCain continues to fight for their entrance to the United States. Neither Senator McCain nor First Lady Laura Bush could be accused of not having America’s best interests at heart in their actions.

We are a nation born of the idea that our values and our principles have the power to make us stronger and safer.

Those who serve America on the battlefield should not have to worry about their family’s safety on the home front.  And banning one religious group is not an expression of our patriotism, but a departure from our values.

Gayle Tzemach Lemmon is a senior fellow at the Council on Foreign Relations and the author of "Ashley’s War: The Untold Story of a Team of Women Soldiers on the Special Ops Battlefield" (Harper, April 2015) and "The Dressmaker of Khair Khana," a New York Times best seller published in March 2011 by HarperCollins, about a young entrepreneur who supported her community under the Taliban. Gayle is a contributor to The Atlantic’s DefenseOne site, writing regularly on national security and foreign policy issues.  Follow her on Twitter @gaylelemmon.