She is among a handful of Republicans to recently break ranks with Gov. Brian Kemp, who appointed Loeffler to the seat in December over Collins and other applicants in part because he hoped she could appeal to suburban women who have fled the party.
Handel, a former Georgia secretary of state, is one of the most prominent women in the Georgia GOP. She defeated Democrat Jon Ossoff in a nationally-watched 2017 special election to represent Atlanta’s northern suburbs in Congress before falling to McBath a year later.
She's also honed a reputation as one of the state's most vocal anti-abortion advocates, an issue that helped shape her previous bids for Congress. She's expected to help Collins counter the state and national anti-abortion groups that have backed Loeffler's campaign.
Handel’s endorsement comes as Loeffler, a former financial executive who is self-financing her campaign, faces more scrutiny over her stock transactions and her ties to Atlanta-based Intercontinental Exchange, the financial trading platform her husband runs.
She announced late Wednesday that she stepped down from a U.S. Senate subcommittee that oversees regulations of some exchanges owned by the company, shortly after she disclosed documents that revealed she got a $9 million payout from the firm before she was sworn in.
Loeffler also opted to dig deeper into her bank account this week to try to pivot her coronavirus message, with plans to spend about $4 million to air a trio of ads that highlights her response to the disease and blasts scrutiny of her stock market moves as "liberal lies."
She has promised to spend at least $20 million to defend the seat in November’s special election, when she’ll face Collins and 19 other challengers in a free-for-all with no party primary to filter out nominees. That race will almost certainly end in a January runoff between the two top finishers.
Her candidacy has sharply divided Georgia Republicans at a time when Democrats are aiming to upend GOP control of the state.
Besides Kemp, Loeffler's main supporters include Lt. Gov. Geoff Duncan and the National Republican Senatorial Committee. She also has nabbed endorsements from several national figures, including former U.S. House Speaker Newt Gingrich and ex-U.N. Ambassador Nikki Haley.
Collins has responded with recent endorsements from U.S. Rep. Drew Ferguson -- the first Republican member of Georgia's congressional delegation to take sides – as well as Public Service Commissioner Bubba McDonald.
Several law enforcement officials have also endorsed his campaign, as well as a handful of congressional contenders in metro Atlanta and north Georgia.