Tulsi Gabbard keeps making her fellow Democrats nervous.

The Hawaii congresswoman and Democratic presidential candidate appeared on Tucker Carlson's show on Fox News. She wrote for the conservative-leaning editorial pages of The Wall Street Journal.

She denounced Hillary Clinton as the "personification of the rot that has sickened the Democratic Party for so long." And facing a stiff primary challenge for her congressional seat, she recently announced her retirement from Congress.

That's feeding fears among party leaders and pundits that Gabbard isn't necessarily aiming to win a Democratic primary but is laying the groundwork to run as a third-party candidate. Such a scenario, they fear, could slice off just enough support from the ultimate Democratic nominee that President Donald Trump could win reelection.

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Gabbard repeatedly denies planning an independent candidacy, as she did Wednesday when she told ABC's "The View" that she's "running to build a new Democratic Party."

Tom Perez, the chairman of the Democratic National Committee, also sought to quell the rumors Wednesday.

"Tulsi Gabbard and every single candidate running for president understands that it's not about them," he told reporters, noting that Gabbard is among the Democrats who have pledged not to run as a third-party candidate. "It's about something much bigger."

But the anxiety isn't going away.

Often expressed privately for fear of pushing Gabbard further from the party, the concerns mirror the handwringing over the abortive presidential bid by former Starbucks CEO Howard Schultz earlier this year. Then, Democrats feared Schultz would peel off enough affluent, suburban voters to reelect Trump. Now, they worry Gabbard's vocal anti-interventionist stance could do the same with younger liberal voters and others unhappy with the Democratic establishment.

Trump was able to win in 2016 with a minority of the popular vote in part because those who disapproved of him in a handful of battleground states split their votes between Clinton and third-party candidates, giving an unusually large share to the Green Party's Jill Stein and the Libertarian Party's Gary Johnson.

Democrats fear a repeat. Only this time, Gabbard, a 38-year-old Samoan-American congresswoman with an unusual mix of political views who has participated in three of the Democrats debates and, on Wednesday, qualified for a fourth, could draw far more attention than Stein and Johnson did.

Some political analysts say Democratic worries may be excessive.

"This is something that's significantly fueled by the 2016 experience," said Josh Putnam, a political scientist who carefully tracks presidential elections through the site FrontloadingHQ.com.

During elections for open presidential seats, third-party votes tend to spike. But during an incumbent president's reelection campaign, they usually dwindle.

In 2000, Green Party candidate Ralph Nader netted 2.74% of the popular vote and was blamed by Democrats for tipping Florida, and the presidency, to Republican George W. Bush. Nader ran again in 2004 during Bush's reelection campaign and got less than 0.4% of the vote.

"We've got an incumbent seeking reelection — that triggers partisanship," Putnam said. "Democrats are going to support Democrats, and Republicans are going to support Republicans."

Gabbard would have a hard time running alone as a third-party candidate — she doesn't have the financial resources of a Schultz and would have to spend mightily and work for months to qualify for a spot on 50 state ballots. But if she joined a more established political operation like the Green Party or the Libertarian Party, their volunteers and positions on dozens of state ballots could help her.

Still, time is running out for Gabbard to win the Green Party nomination, said Holly Hart, a party official who sits on the committee overseeing the presidential contest.

"I know a lot of Greens like her a lot," Hart said of Gabbard, but "she'd have to get in in the next couple of months" to make it onto the party's primary ballot in major states like California.

The Libertarian Party, which appeared on all 50 state ballots in 2016, is fairly flexible in its nominating process, according to its executive director, Daniel Fishman. Delegates chosen by its state chapters can select anyone they wish as its presidential nominee during the party convention in May 2020, after almost all states have voted in the Democratic contest.

"Technically, it is very possible that she could come and compete for the nomination," Fishman said of Gabbard.

Gabbard has been causing unease among some Democrats since 2016, when she served as vice chair of the DNC as a nod to her status as a rising young star in the party. But she resigned in protest, saying the party was rigging the presidential primary election for Clinton at the expense of her preferred candidate, Vermont Sen. Bernie Sanders.

Gabbard stood out from other Democrats by criticizing President Barack Obama for not using the phrase "Islamic fundamentalism" to describe terrorism — picking up a GOP attack line — and for being one of two Democratic representatives to vote for a Republican bill to essentially block Syrian refugees from entering the United States for six months.

She drew widespread condemnation for meeting with Syrian President Bashar Assad during the country's civil war and for appearing on RT, Russia's state television network in the U.S.

Still, Gabbard is hard to pigeonhole politically — she's also a civil libertarian and longtime critic of the drug war, supporter of legalizing marijuana and advocate for ending fossil fuel use, all positions that have at various times endeared her to the liberal wing of the Democratic Party.