Former Rep. Tulsi Gabbard (D-Hawaii) on Sunday warned Donald Trump that Kamala Harris “is not to be underestimated” in the ABC News debate next week.

In an interview with CNN’s “State of the Union,” Gabbard was asked to assess whether the vice president could prove a challenge for former President Trump on the debate stage as Harris’ campaign has noted they expect him to be a “formidable opponent.”

“Yeah, I think Kamala Harris has a lot of experience,” Gabbard replied. “She is not to be underestimated.”

Gabbard argued the debate will offer an opportunity for voters to compare and contrast the two candidates’ records, noting Harris’ four years of service as vice president in Joe Biden’s administration.

Gabbard has been helping Trump prepare for the Sept. 10 face-off. The former Hawaii congresswoman shared the stage with Harris during a debate amid the 2020 Democratic presidential primary, when she also ran for president. She dropped out in March 2020 and offered Biden her “full support.”

In her CNN interview, Gabbard suggested that Trump should focus on the evolution of Harris’ policy positions since she was a candidate in the primary.

“If I can be helpful to President Trump in any way, it really is just sharing experience that I had with her on that debate stage in 2020 and, frankly, helping to point out some ways that Kamala Harris has already shown that she is trying to move away from her record, move away from her positions, and how that contradicts the positions and statements that she is making now that she is the Democratic nominee,” she told CNN.

Gabbard, who announced her departure from the Democratic Party in October 2022, endorsed Trump last month despite previously calling him “corrupt.”

Gabbard was reportedly on Trump’s vice presidential shortlist before he eventually picked Ohio Sen. JD Vance (R). Trump has named her as a member of his presidential transition team, and Gabbard also moderated a town hall with the former president in Wisconsin last week.

Gabbard has previously signaled interest in the prospect of serving in a potential second Trump administration, potentially as secretary of state or defense, but told CNN’s Dana Bash she hasn’t had a chance to discuss the possibility with Trump himself as she remains focused on helping him secure victory in November.

Meanwhile, Trump has again left the door open to pulling out of the ABC debate last minute, claiming the network is unfair and has “terrible” journalists.

“ABC is probably the worst in terms of fairness,” Trump told Fox News’ Mark Levin in an interview broadcast Sunday.

The debate is set to take place in Philadelphia and will be moderated by David Muir and Linsey Davis.