In the letter – which Hasan's attorney, retired Army Col. John Galligan, provided to Fox News – Hasan triumphantly declared, "We Have Won!!!" Hasan, who fatally injured 13 and wounded more than 30 others, wrote the letter from death row at Fort Leavenworth Prison.
"All-Praises be to All-Mighty Allah! Congratulations on your victory over those who hate for the Laws of All-Mighty God to be supreme on the land," Hasan wrote in a message he directed Galligan to forward to Taliban leadership.
"I pray to Allah that He helps you implement Shariah Law fully, correctly, and fairly," Hasan added. Shariah refers to Islamic law, interpretations of which vary widely. Extremists like Hasan and the Taliban interpret Shariah harshly, rejecting many modern conceptions of human rights, especially women's rights and religious freedom.
"We must learn from the nations of the past and not let our wretchedness overcome us thus earning His (God's) wrath," Hasan added. "It is to All-Mighty God we give thanks!"
"The letter from my client Major Nidal Hasan does not come as any surprise – it reflects the deeply held convictions he has for his Islamic faith and his perceived value of Sharia Law," Galligan told Fox News in a statement on Wednesday. "I believe he is pleased to see that the Biden Administration is now seemingly willing to engage with the Taliban as de facto government in Afghanistan."
White House Press Secretary Jen Psaki said the Biden Administration was in "no rush" to recognize the newly-formed Taliban government in Afghanistan, but she hinted that the administration would seriously consider it, depending on the Taliban's actions.
"There's no rush to recognition, and that will be planned dependent on what steps the Taliban takes," White House Press Secretary Jen Psaki said Tuesday. "The world will be watching whether they allow for American citizens, whether they allow individuals to leave who want to, and how they treat women and girls around the country."
Hasan's lawyer mocked the Biden administration.
"While Major Hasan has not changed his opinions about the Taliban, it would appear President Biden has done a complete about-face," Galligan quipped.
Biden faces harsh criticism for sticking to his August 31 deadline for the full withdrawal of U.S. troops from Afghanistan, despite knowingly leaving many Americans behind.
Survivors of the Fort Hood shooting did not take kindly to Hasan's letter.
Former Staff Sgt. Alonzo Lunsford, who survived getting shot seven times and grazed in the head, responded to the letter in an interview with Fox News on Wednesday.
"My response to him, personally, is I give all my praises to my God who taught me to be a forgiving person," Lunsford said. "Allah is not the one who still has him taking in oxygen right now. Allah is not the one who spared his life. Allah is not the one who stopped me from wrapping my hands around his neck when I was less than three feet away from him in the court room."
"He needs to be thankful that he is alive. He needs to be thankful that we did not try him according to Shariah Law," Lunsford continued.
The survivor noted that Shariah Law carries harsh punishments for "people that are blasphemous, people that lie, people who do the things that he did, which are against the true teachings of the Quran. I happen to be fortunate enough to have read the Quran."
"His statement is not only poking the bear, but he’s trying to awaken a sleeping giant," Lunsford added, referencing "the true wrath of our beloved United States of America."
Former Sgt. Howard Ray, a witness to the Fort Hood attack who helped get people to safety as Hasan shot at him, said Hasan's letter to the Taliban should serve as a reminder that radical Islamic terrorism is still a threat.
"I think it's a stark reminder that terrorism is still alive, obviously abroad and here at home," Ray told Fox News on Wednesday. He said Nadal Hasan's decision to embrace the Taliban is not a surprise, but it does represent a "manifestation" of a broader threat.
"Frankly, it kind of worries me because Islamic extremists, they hold on to that," Ray noted. "Is that a call to others to maybe initiate something here at home? I think it has that potential."
Ray faulted the Biden administration for being "ill-equipped," not "ready to deal with" the broader threat of terrorism.
"Just look at November 5, 2009, we're coming up on the 20th anniversary of 9/11," he said. "It just takes the will of a few select people to destroy the lives of others."
While Ray warned about the threat of radical Islamic terrorism, he argued that "it's not the people who understand religion for what it's supposed to be. It's those who take extreme positions and then act on those extreme ideologies that we have to worry about."
He said the anniversary of 9/11 is "a time to reflect on those who've lost their lives but we need to constantly remember what it was that drove those people to do those heinous acts, and it was in this case Islamic extremism. We need to keep a watchful eye on that."