CHICAGO - While Democratic luminaries including the Obamas enthusiastically support Kamala Harris for US president at their party's convention, an unlikely band of rebels is joining the effort: Republicans urging fellow conservatives to ditch Donald Trump.

The message is nothing new -- several Republicans have spoken out against Trump over the years. But their presence at this week's carefully orchestrated Democratic confab has amplified the call for conservatives and independents to reconsider their election choice in November.

"Let me be clear to my Republican friends at home watching," Geoff Duncan, the former lieutenant governor of Georgia where Trump sought to overturn the results of the 2020 election, said Wednesday from the convention stage.

"If you vote for Kamala Harris in 2024 you're not a Democrat, you're a patriot," he boomed.

Slamming the recently convicted -- and twice-impeached -- former president as "a direct threat to democracy," Duncan said he was aiming his remarks at the millions of Republicans and independents he knows are "sick and tired of making excuses" for Trump.

"These days our party acts more like a cult, a cult worshipping a felonous thug," said Duncan.

Multiple Republicans have offered similar messages in Chicago, as the Harris campaign seeks to peel off as many Republicans and independent voters as possible in an election that is going down to the wire.

Former White House communications director Stephanie Grisham, who had close access to Trump, took the stage Tuesday slamming her ex-boss as a liar with "no empathy, no morals and no fidelity to the truth."

"I saw him when the cameras were off. Behind closed doors, Trump mocks his supporters, he calls them basement dwellers," she said.

Grisham, who was also first lady Melania Trump's chief of staff, mentioned how she had gone from "a true believer" to a disaffected close advisor who wanted out, and recalled a turning point during the 2021 US Capitol riot by Trump supporters.

"On January 6 I asked Melania if we could at least tweet that while peaceful protest is the right of every American, there's no place for lawlessness or violence," Grisham said.

"She replied with one word: 'No.'"

Grisham resigned that day, "because I love my country more than my party," she said, to loud applause, adding that Harris "has my vote."

- 'Kidnapped by extremists' -

John Giles, mayor of Mesa, Arizona, and a self-described "lifelong Republican" who claims late senator John McCain as his hero, was equally blunt.

He told the convention his Republican Party "has been kidnapped by extremists and devolved into a cult: the cult of Donald Trump."

Giles's message to Americans like him who are in the political middle: "John McCain's Republican Party is gone, and we don't owe a damn thing to what's been left behind."

Organizers aired a video Wednesday showing former Trump voters explaining why they were flipping to Harris.

"I made a grave mistake," Florida voter Rich Logis said via video about how he had jumped headlong into Trump's MAGA movement. "But it's never too late to change your mind," Logis said.

Olivia Troye, a former counter-terrorism advisor for Trump's vice president Mike Pence, addressed the convention, while high-profile Republican never-Trumper Adam Kinzinger, an ex-congressman, takes the stage Thursday, the closing night.

Trump frequently assails such critics as traitors to the cause, and it remains unclear how persuasive they will be.

David Urban, a Republican advisor to Trump's 2016 campaign, dismissed any substantial impact.

But he told CNN the appearance by Georgia's Duncan "may give people permission to vote for Kamala Harris" in the state.

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