2024 election live updates: Obama and Harris rally together in Georgia; Trump campaigns in Arizona

At least a dozen voters in Mesa County, Colorado, had their ballots stolen and fraudulently filled out without them knowing, Secretary of State Jena Griswold announced Thursday.

After the stolen mail-in ballots were returned to the clerk's office via the Postal Service, the state's voter signature verification system flagged discrepancies with the signatures on some of the ballots, she said. When election officials reached out to the voters to offer them a chance to "cure" the issue, the voters informed the officials that they hadn't voted, according to Griswold.

Three of the stolen ballots that passed the signature verification process were successfully cast.

"This attempt at fraud was found and investigated quickly because of all the trailblazing processes and tools Colorado has in place like signature verification, ballot tracking, and the curing process," Griswold added. "Every eligible Colorado voter will be able to make their voice heard this election."

The Mesa County District Attorney's Office is investigating the fraud scheme.

Earlier this month, Tina Peters, the former Mesa County Clerk and Recorder, was sentenced to nine years in prison for leading a security breach of the county's election system.

Peters, a Republican, was convicted for giving an individual affiliated with MyPillow CEO Mike Lindell, a Trump ally, access to the election software she used for her county. Screenshots of the software appeared on right-wing websites.

Harris running mate Minnesota Gov. Tim Walz made a quick visit to a canvassing event at the Pitt County Democratic headquarters in Greenville, North Carolina, on Thursday afternoon and delivered a stump speech focused on energizing volunteers.

He also repeated his criticism of Trump wishing he'd had generals like those of Adolph Hitler.

"She's got a to-do list, he's got an enemies list," Walz said, contrasting Harris and Trump.

Walz said that just when he thought Trump "couldn't get any lower," the accounts of John Kelly, the former Trump chief of staff and Marine four-star general surfaced.

"The idea that the people closest to him, four-star generals, telling us that that guy's fantasizing behind closed doors, that he wished he had Adolf Hitler's generals. That is so damn disqualifying," he said.

Walz shifted to Trump ally billionaire Elon Musk and repeated an insult that he hurled during a campaign stop in Madison this week calling him a dips***. Walz joked that was a Minnesota term.

"I think that's a North Carolina term, too, right?" he asked. "I said that wasn't a pejorative. That's just it, standing up there as the richest man in the world. Instead of putting your money in to help people and end homelessness or end hunger or do all that you're looking for."

In the final campaign stretch, ABC News Senior White House Correspondent Selina Wang reports she is hearing the phrase "nervous optimism" from multiple Harris campaign officials and donors.

Harris' team knows this race is still locked in a dead heat, but the optimism comes from the Democrats' "strong ground game." The hope is that their better organization and canvassing on the ground will tip the scales in their favor, but they're keenly aware that Republicans could outperform in the polls as Trump did in 2016.

The Harris campaign is doubling down on peeling away disaffected Republicans. As one donor put it: "We're now the party of AOC and Dick Cheney -- that's crazy."

While Harris started her campaign with a message about joy and the future -- with her catchphrase "we're not going back -- Harris is ending her campaign with a message that sounds a lot like President Joe Biden's when he was still in the race: that Trump is a fundamental threat to democracy.

Her campaign is betting this will make the difference with those swing voters, but the risk is overemphasizing the anti-Trump message versus a positive message about a future Harris presidency.

But campaign sources highlight the fact that Harris has all the big superstar surrogates who can help make the pitch in other ways, including Barack and Michelle Obama, Bill Clinton, Magic Johnson, Beyonce, Bruce Springsteen, Eminem and more while Trump has Elon Musk.

One campaign source, when asked what made them most nervous (such as the gender gap, turnout from Black men or something else), said: "Everything is on the margins, so everything makes me nervous."

Gov. Tim Walz told organizers and volunteers at Duke University on Thursday that their youth vote in the battleground state could make a difference for "generations to come."

"What a privilege to be in this moment," he said. "They are going to write about Americans who stood up in this moment and said "hell no" to this, the tendencies of totalitarianism, and the division and racism, the hatred, the misogyny, everything else that goes with that. You're going to get asked, 'When you're my age, what did you do?' And your answer is, 'I did every damn thing possible.'"

Walz's message seemed more urgent than usual, with just 12 days until the election.

At first, Walz said he didn't want to put "fear" in the students. But he later asserted, while highlighting Trump's "enemy from within" remarks, that the former president would come for any of his political enemies.

"I'm on the top of his list, but don't kid yourself, you're somewhere on that list, too, if you disagree with these people," Walz said.