Originally Published: 25 AUG 21 06:00 ET

Updated: 25 AUG 21 13:54 ET

By Alex Rogers, CNN

(CNN) -- Herschel Walker, the former football star, announced his campaign for US Senate in Georgia on Wednesday, after months of speculation marked by both former President Donald Trump's public encouragement and some Republicans' rising concerns about the political newcomer's ability to win a crucial seat.

"Our country is at a crossroads, and I can't sit on the sidelines anymore," said Walker in a statement. "In the United States Senate, I will stand up for conservative values and get our country moving in the right direction. It is time to have leaders in Washington who will fight to protect the American Dream for everybody."

He released a video later Wednesday displaying his rise from humble roots in Wrightsville to winning the Heisman Trophy on the University of Georgia football team in 1982. In his high school Trojans gear, Walker ran, worked out and preached that "you only fail if you give up."

"I'm a kid from a small town in Georgia who lived the American Dream, and I'm ready to fight to keep that dream alive for you too," Walker said.

Some Trump allies have advocated for Walker, saying that having a celebrity, conservative African-American would amount to an ideal candidate against Georgia Democratic Sen. Raphael Warnock, one of three Black senators and the senior pastor of Ebenezer Baptist Church in Atlanta.

"Herschel Walker understands the predicament our country is now in and the importance of those who love this country to step forward and do what it takes to save it," said Randy Evans, a Georgia lawyer and former US ambassador to Luxembourg in the Trump administration.

But other GOP strategists and lawmakers from Georgia to Washington, DC, are deeply worried about Walker's campaign, fearing that Walker could cost the GOP a winnable seat. Three Republican candidates -- Georgia agriculture commissioner Gary Black, construction firm owner Kelvin King and banking executive and Navy veteran Latham Saddler -- have already announced their campaigns.

Earlier this summer, Senate Minority Leader Mitch McConnell even suggested to allies that former Georgia Sens. David Perdue and Kelly Loeffler, both Republicans, should take another look at running again, after their narrow losses in January flipped the Senate to Democratic control.

Some Republicans were alarmed by a recent Associated Press report detailing Walker's past, including that he threatened violence against his ex-wife. The AP also found that Walker had greatly exaggerated how much revenue his company -- Renaissance Man Food Services -- earned and how many people it employed. And until recently, Walker lived in Texas and did not have a political operation in Georgia.

"I do not know a single credible Republican strategist in Georgia or Washington who thinks he can be beaten in the primary," Erick Erickson, a conservative radio host based out of Atlanta, wrote Wednesday. "I do not know a single credible Republican strategist who thinks he can win the general."

Walker's campaign said he succeeded as a professional athlete and in his various businesses. He "dedicated his life to helping others with similar struggles" to his dissociative identity disorder, and visited "thousands of troops and patients struggling with mental health" over the years, the campaign also highlighted.

"America is the greatest country in the world, but too many politicians in Washington are afraid to say that," said Walker. "Where else could a poor kid from a small town in Georgia become valedictorian of his high school, earn the Heisman Trophy, play professional football, represent the United States in the Olympics, and become CEO of multiple companies? I have lived the American Dream, but I am concerned it is slipping away for many people."

In his video, Walker tried to turn his lack of experience in politics into an asset, and did not mention his mental health struggles, even though he has been open about them.

"The politicians pit American against American, rich versus poor, black versus white, urban versus rural," Walker said. "I don't believe in that garbage. It's a lie."

He also described why he's a Republican.

"I'm a conservative not because someone told me to be," said Walker. "I'm a conservative because I believe in smaller government, a strong military, personal responsibility, and making sure all people have the opportunity to pursue their dreams. That's an America worth fighting for."

The race against Warnock could decide the Senate. Democrats in the upper chamber have the slimmest of majorities -- 50-50 -- held only by Vice President Kamala Harris' tie-breaking vote. Warnock beat Loeffler in 2020 by two points.

"Walker's entrance into Georgia's chaotic GOP Senate primary is the nightmare scenario that Republicans have spent the entire cycle trying to avoid," said Georgia Democratic party spokesman Dan Gottlieb. "By the end of this long, divisive, and expensive intra-party fight, it'll be clear that none of these candidates are focused on the issues that matter most to Georgians."

Walker has a long relationship with the former President going back to 1984, when Trump -- the then-owner of the United States Football League's New Jersey Generals -- gave Walker a contract extension.

They stayed in touch. Donald Trump Jr. recounts in his book "Triggered" that he went to Disney World when he was 6 with Walker's family, and Walker would visit the Trumps at their house in Greenwich, Connecticut. Walker later appeared on NBC's "The Celebrity Apprentice" with Trump and encouraged his 2016 and 2020 presidential bids.

In December, Walker tweeted a video supporting Trump's effort to overturn his loss to then-Democratic presidential candidate Joe Biden. Trump responded, "Herschel is speaking the truth!"

This story has been updated with additional developments Wednesday.