(PHOENIX) -- Republican Kari Lake, a popular former local news anchor, self-described "MAGA Mama Bear" and staunch ally of former President Donald Trump, launched a campaign for the U.S. Senate at a rally in Scottsdale, Arizona, on Tuesday night, nearly a year after losing the state's gubernatorial race -- a defeat she still refuses to concede.
Sen. Kyrsten Sinema, who left the Democratic Party last year to become an independent, has not yet said whether she'll run for reelection, but Lake is already preparing for a three-way race against Sinema and Rep. Ruben Gallego, the likely Democratic nominee.
ABC News previously reported that Democrats and Republicans alike were expecting an unpredictable contest in a state where a third of the electorate identifies with neither party. The winner could determine the balance of control in one half of Congress; currently Democrats hold the Senate 51-49.
In a statement last month, Lake attacked Gallego and Sinema as "a rubber stamp" for President Joe Biden's agenda.
"Both of them have been in Congress for a combined two decades and have failed to secure the border here in Arizona," she argued.
In announcing his own Senate bid earlier this year, Gallego said, in part, "I'm running for the U.S. Senate because the rich and the powerful don't need any more advocates in Washington -- but families who can't afford groceries do."
Sinema has touted her track record in Congress: "I get there every day to put my head down and just focus on solving problems," she said in a local radio interview in January.
Both she and Gallego have said they are focused on border policies.
Lake filed paperwork with the Federal Election Commission and Arizona secretary of state's office last week on her intent to run, and she met with several Republican senators on Capitol Hill.
"We have had productive conversations with Kari Lake and her team," Steve Daines, R-Mont., the chairman of the National Republican Senate Committee, told ABC News in a statement. "She is a talented campaigner with an impressive ability to fire up the grassroots."
Lake also had meetings with Texas Sen. John Cornyn and Arkansas Sen. Tom Cotton and was spotted walking across the Capitol with Wyoming Sen. John Barrasso, the third-ranking member in the Senate Republican leadership.
Democrats, meanwhile, argue Lake is a losing candidate with Michigan's Gary Peters, the Democratic Senatorial Campaign Committee Chair, calling her bid "Senate Republicans' worst nightmare."
"Even Republicans didn't want Lake to run because voters rejected her before, and they'll do so again in 2024," Peters said in a statement.
Gallego spokeswoman Hannah Goss said in a statement ahead of Lake's campaign launch that "her extremism should disqualify her from public office — and it will. Again." Goss pointed to Lake's support for abortion restrictions as well as her criticism of her own election loss.
Lake will face a primary contest against former Pinal County Sheriff Mark Lamb, who supported Lake's bid for governor last year.
"I wouldn't sleep on Mark Lamb," said Barrett Marson, a GOP strategist in Arizona who isn't working with a campaign so far this cycle. "He's a conservative, but he's not Kari Lake, and she only wants to talk about election denialism, something that the broader Arizona electorate just does not care about."
Rick Gorka, an adviser to Lamb's campaign, likened Lake to "Arizona's version of [Democrat] Stacey Abrams," referring to another high-profile but unsuccessful gubernatorial candidate -- in Georgia.
"While she has been everywhere but Arizona, Sheriff Mark Lamb has been serving the people, fighting to secure the border and meeting with voters who deserve a proven, conservative winner," Gorka said in a statement to ABC News.
Lake mirrors Trump
Lake's campaign for governor burnished her profile among conservatives and earned her widespread attention, in large part for how she embraced the style and policies of the former president, including vowing to declare an invasion at the southern border and regularly sparring with the news media even as she readily made herself available to reporters.
Lake also often repeated Trump's baseless claims that the 2020 election was fraudulent and she sought to delegitimize her own narrow loss to now-Gov. Katie Hobbs. (The courts rejected Lake's claims.)
After defeating Karrin Taylor Robson, widely thought of as the GOP establishment candidate, in the 2022 Republican gubernatorial primary, Lake quickly built up a following among the conservative base but also alienated supporters of the late Arizona Sen. John McCain, saying her movement successfully "drove a stake through the heart of the McCain machine."
Republicans flocked to Arizona to fuel the enthusiasm for the political newcomer, including Virginia Gov. Glenn Youngkin, South Dakota Gov. Kristi Noem and Florida Gov. Ron DeSantis, who Lake has since soured on amid his 2024 White House challenge to Trump.
Prominent names campaigned against Lake as well, including former Republican Rep. Liz Cheney, who invested in ads against Lake in Arizona, and former President Barack Obama, who told a packed gym of supporters in Phoenix during early voting in 2022 that elected office "is about more than snappy lines and good lighting."
While Hobbs ran a low-key campaign by comparison, facing criticism for refusing to debate Lake, she ultimately won by just over 17,000 votes. Experts called it an example of how midterm voters in various parts of the country appeared to be turned off by election denialism.
Lake continues to falsely claim victory, despite her challenges over ballot-signature verification efforts and alleged voter fraud failing in court. In July, some of her attorneys were even sanctioned to reimburse Maricopa County $122,200 in legal fees after a federal court determined a lawsuit Lake filed with failed Secretary of State candidate Mark Finchem was "pursuing frivolous constitutional claims."
'Just getting started'
In the months since Hobbs' inauguration, Lake has traveled the country -- to Iowa, Florida, Michigan and more battleground states -- hitting the media circuit as a surrogate for Trump's comeback presidential campaign but also airing her own electoral grievances with her first book, Unafraid: Just Getting Started, in which she falsely calls herself "the lawful governor of Arizona."
"She can win a primary, but I think she'll have the same problem she had in 2022 if she doesn't move off of her election denials," said Marson, the Republican strategist. "A normal, conservative Republican could easily take this race. But a Donald Trump acolyte like Kari Lake will find a very difficult path forward."
Arizona is among the handful of Democratic-held Senate seats that Republicans are targeting in 2024. It was also where President Joe Biden saw his most narrow battleground win in 2020.