David Brat addresses voters at the Henrico County Republican Party breakfast meeting April 26 in Glen Allen, Va. (Jay Paul/Getty Images)

Republican congressional candidate Dave Brat replaced his campaign manager after just three weeks on the job, adding to the growing pains for the political newcomer who toppled former House majority leader Eric Cantor.

Phil Rapp, an aide to state Sen. William M. Stanley Jr. (R-Franklin), will take the reins from Amanda Chase, who once worked for Cantor, the Brat campaign confirmed Tuesday. Like Chase, Rapp has never run a congressional campaign.

“As a long-time friend, Amanda really stepped up and helped me when I needed her most — coming in as my transition campaign manager until we could put our full team together. I understand she needs to return to her business and other pursuits, and I will always be grateful for her service,” Brat said in a statement.

Brat has avoided the media spotlight since his unexpected win over Cantor (R), who was in line to be the next speaker of the House.

Brat stumbled in his first major interview the day after the primary when NBC reporter Chuck Todd asked him to clarify his positions on several foreign policy issues. Since then, the candidate has kept a relatively low profile.

Chase’s departure is being seen by some as an early misstep for Brat, even though he is favored to win the heavily Republican district, which stretches from suburban Richmond northwest toward the Shenandoah Valley.

Some members of Brat’s party have characterized his campaign as being in “disarray” and have expressed amazement that his organization took out the majority leader.

Brat, an economics and ethics professor at Randolph-Macon College, announced Chase’s hire last month in one of his first public appearances after the primary.

At the time, Brat said she would work though the “transition” to the general election, and he would not say if she would stay on through November.

Rapp is a retired executive from Tredegar Corp., a ­Richmond-based manufacturing company. As a senior adviser and volunteer coordinator during the primary campaign, he was in charge of the grass-roots field operation that many credit with making the difference in Brat’s defeat of the entrenched incumbent.

Zachary Werrell, who served as Brat’s campaign manager during the primary and attracted attention for his young age — 23 — and for running the campaign with an antiquated flip phone, has since left the campaign. Asked Tuesday if it was his decision to leave, Werrell declined to comment.

Chase, who was political director for Susan Stimpson in her failed bid for the GOP nomination for lieutenant governor in Virginia last year, will return to work at the financial planning firm she runs with her husband, Brat campaign spokesman Brian Gottstein said.

“She has a heart for the grass roots and a great deal of campaign experience,” Brat said when he hired her. “To her credit, months ago, when I was the underdog, she stated publicly that I was a credible candidate and contender in this race.”

Brat, who spent six years as special legislative assistant to state Sen. Walter A. Stosch (R-Henrico), has focused on three main issues: repeal of the Affordable Care Act, stopping illegal immigration and reducing the debt and deficit.

Though he has shied away from saying what his stunning win means for the Republican Party on a national scale, Brat’s supporters say Cantor was disconnected from the district and too open to compromise with the Obama administration, despite his fiery rhetoric against the president.

Brat will face Democrat Jack Trammell, also a professor at Randolph-Macon, in the fall.

The campaign also announced that Brat had hired Tim Edson as a general consultant. Edson ran Rep. Allen B. West’s (R-Fla.) unsuccessful reelection campaign in 2012 and worked for Stimpson alongside Chase.