A Georgia grand jury investigating President Trump’s efforts to change the election outcome in that state in 2020 will reconvene at Atlanta this week and is expected to hear, among others, from the former lieutenant governor there as prosecutors, after more than two years of investigation, finally begin making their case to the jury.

Geoff Duncan, a Republican, confirmed on Twitter Saturday that he is one of the witnesses that has been called by Fulton County district attorney, Fani Willis, in her investigation. He said on Twitter that he will testify on Tuesday, an indication that Ms. Willis is preparing to begin making her case to the jury.

“I look forward to answering their questions around the 2020 election,” Mr. Duncan said. “Republicans should never let honesty be mistaken for weakness.”

While a portion of Ms. Willis’ case is said to focus on Mr. Trump’s attempts to put forward a fake slate of electors there and persuade Secretary of State Brad Raffensperger to “find” him enough votes to overturn the outcome of the election, attention also has been focused on an unauthorized breach of the state’s voting system machinery in rural Coffee County in January 2021.

New evidence has reportedly surfaced indicating that the county was ground zero for efforts by Trump supporters to find evidence of illegality in the counting of the vote in Georgia.

CNN reported Sunday that Ms. Willis has text messages and emails directly connecting Mr. Trump’s legal team to the Coffee County breach. The evidence purports to show that forensics experts hired by Mr. Trump and his supporters copied voting system components and software from Dominion Voting Systems machinery and shared the information with others around the country seeking evidence of fraud.

The Trump team was invited to Coffee County — which Mr. Trump won that year by a landslide — by a local elections official, Misty Hampton. Far from merely being a homegrown effort by local supporters of the president, which has long been known about and is currently under investigation by the Georgia Bureau of Investigation, the new evidence suggests that the illegal breach was conducted with the support and encouragement — if not oversight — of Mr. Trump’s legal team, including Mayor Giuliani.

Several people involved in the voting systems breach are among those being investigated by Ms. Willis and may be charged by the same grand jury investigating Mr. Trump.

Speaking on his own social media platform, Truth Social, Mr. Trump repeated his oft-made assertion that no election interference occurred in Georgia after the 2020 election and suggested that Ms. Willis, to whom he referred as “Phoney Fani,” would better serve the people of Atlanta by focusing on crime in that community.

“The only Election Interference that took place in Fulton County, Georgia, was done by those that Rigged and Stole the Election, not by me, who simply complained that the Election was Rigged and Stolen,” he wrote. “We have Massive and Conclusive Proof, if the Grand Jury would like to see it. Unfortunately, the publicity seeking D.A. isn’t interested in Justice, or this evidence.”

If Mr. Trump is indicted in the Georgia probe, it will mark the fourth indictment of the president in recent months. In addition to two indictments handed down by special prosecutor Jack Smith — over classified documents hoarded at his Mar-a-Lago estate and his actions to incite the riot at the Capitol on January 6, 2021 — Mr. Trump also faces charges in New York over hush money payments to an adult actress. Mr. Trump is the first American president to ever be indicted.