WASHINGTON - A series of tweets from President Donald Trump dashed Nicolas Talbott's dreams. Now he's fighting back.

The 23-year-old transgender man saw joining the Air Force National Guard as a way to pursue a global security and counterterrorism career. After graduating from Kent State University in 2015 with a degree in sociology and criminology, he'd worked jobs including truck and bus driving.

The one thing standing in his way was the military's ban on transgender troops. He was elated when the Pentagon ended that policy last year, citing a RAND Corporation study that said allowing open service by transgender people would have minimal impact on military readiness and health care costs.

But his elation was short-lived. As Talbott prepared over the summer for the vocational and fitness exams required for enlistment, Trump took to Twitter to announce the ban's reinstatement.

"Our military must be focused on decisive and overwhelming victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail," Trump declared, to Talbott's chagrin.

After consultation with my Generals and military experts, please be advised that the United States Government will not accept or allow...... — Donald J. Trump (@realDonaldTrump) July 26, 2017

....Transgender individuals to serve in any capacity in the U.S. Military. Our military must be focused on decisive and overwhelming..... — Donald J. Trump (@realDonaldTrump) July 26, 2017

....victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail. Thank you — Donald J. Trump (@realDonaldTrump) July 26, 2017

Trump later issued a more detailed policy statement that said the prior administration "failed to identify a sufficient basis to conclude" that ending the transgender ban "would not hinder military effectiveness and lethality, disrupt unit cohesion, or tax military resources." He said more study is needed and ordered a return to the policies in place before June 2016 "until such time as a sufficient basis exists upon which to conclude that terminating that policy and practice would not have the negative effects discussed above."

In an interview, Talbott said he was "shocked and devastated" by the reversal.

"It felt like the rug had been pulled right out from under me," said Talbott. "This is what I was planning to spend my life doing. This was going to be my livelihood and career and suddenly my entire future had been ripped away from me."

Instead of enlisting in the military as he planned, Talbott enlisted as a plaintiff in one of the federal lawsuits to overturn the ban. He heard about the case through transgender veterans' forums on social media. He says he participated to "make a difference in my own life and those of people in similar situations to myself."

The California case in which Talbott is a plaintiff - Stockman v. Trump - contends that the ban "violates the U.S. Constitution's guarantees of equal protection, due process, and freedom of expression." It also says that discriminating against individuals who have undergone or wish to undergo a gender transition is literally discrimination because of sex.

The Trump administration has asked that the case in the United States District Court for the Central District of California be thrown out, arguing it's "premature" to ask the court to judge whether a future government policy is constitutional, because the changes haven't happened. It noted that Trump ordered the Secretary of Defense to review the policy and stated no changes would occur until after March 23, 2018. Consequently, it argued the plaintiffs haven't been injured and lack standing to challenge the policy.

"The public interest obviously would be harmed if an injunction precluded the President and Secretary of Defense from receiving expert advice," an administration legal brief said.

Talbott's lawyers countered that they have a right to challenge an upcoming policy change and the administration's work to implement the ban doesn't make it "any less subject to challenge, or its harms any less immediate." A hearing in the case is scheduled for Nov. 20.

Similar challenges to the transgender troop policy have been filed in federal courts in Maryland, Washington and the District of Columbia by existing transgender troops who fear ejection from the military, as well as transgender people like Talbott who hope to enlist.

On #VeteransDay, our courageous #transgender #military ban plaintiffs share their message of honor and respect for those who have served. pic.twitter.com/WvdqvGsiZW — National Center for Lesbian Rights (@NCLRights) November 11, 2017

A preliminary injunction issued last month in the District of Columbia case has halted the military from enforcing the transgender ban while the case persists. It ordered temporary reinstatement of policies that existed before Trump's statements.

If the injunction remains in place while the cases go through the legal system, the Pentagon would not be able to discharge current transgender personnel while the cases are pending, and transgender people would be able to enlist in the military next year, said Jennifer Levi, an attorney in both Talbott's case and the District of Columbia case. But she said the Trump administration could still appeal and have the injunction overturned.

She said transgender people who serve in the military must meet the same qualifications and fulfill the same job responsibilities as everyone else, and have been doing so "admirably and courageously for decades." She said the military decided to allow open service by transgender people after years of study, and Trump's sudden reversal "is not grounded in military policy."

She predicts the issue will be resolved in the U.S. Supreme Court unless the administration changes its stance.

"People can't be excluded from participating in civic institutions simply because of who they are, and having nothing to do with their ability to contribute," said Levi.

As he waits to be allowed to enlist, Talbott says he's working as a substitute teacher and may enroll at Kent State again for another degree.

He says he's always been interested in military service, and would love the structure of the military service, as well as the benefits and career opportunities it provides. He said he'd like to work in military security or intelligence and counterintelligence.

He says he believes serving in the military would be a good environment for a transgender person because it is "all about brotherhood and lifelong friendships and bonds, knowing you can depend on a person no matter what, regardless of race, gender, sexual orientation or religion."

"The culture of the military as a whole is based on brotherhood, teamwork, putting aside your differences in civilian life and coming together to make the greatest team in the world," says Talbott.