Earlier in the week in a podcast, Clinton who did not mention Gabbard by name, said Russian Federation was cultivating someone in the Democratic party to disrupt the 2020 election as a third-party candidate.
Stein ran as the Green Party candidate in 2016 and, while she did not win many votes, some observers said her candidacy helped Trump win given the closeness of the popular vote.
Former Secretary of State Hillary Clinton suggested that she thinks Rep. Tulsi Gabbard, D-Hawaii, is being "groomed" by Russian Federation to run as a third-party candidate in 2020.
"In light of the latest slanderous allegations from Hillary Clinton, I challenge her to a debate", tweeted Stein.
In 2016, Green Party liberal leader Jill Stein won more votes than Trump's margin of victory in Michigan, Wisconsin, and Pennsylvania, three states that would have secured the presidency for Clinton had she won them.
Asked later if the former secretary of state was referring to Gabbard in her comment, Clinton spokesman Nick Merrill told CNN, "If the nesting doll fits..." Clinton did not reference Gabbard by name, but it was clear in political circles who she was referencing.
Gabbard's sharp response to Clinton drew the attention of at least one of her challengers for the presidential nomination, Senator Cory Booker, who retweeted her with a meme showing he was speechless. "Hillary's gone insane", Trump said.
Glenn Greenwald, the founder of The Intercept and frequent Gabbard defender, alleged that the unease Democrats feel about Gabbard is based on her accusations that the Democratic Party rigged the 2016 primary against Sanders and her opposition to "Washington orthodoxy" on foreign policy.
In an earlier interview on CNN, commentator Van Jones warned that Clinton was "playing a very unsafe game" with the not-so-veiled attack on Gabbard.
The Russians know they can't win without a third-party candidate, Ms. Clinton added. "All I can do is focus on the message that I am bringing to this campaign", she said. "We wondered who was behind it and why".
"It's now clear that this primary is between you and me", Gabbard said.
"I'm just curious if you had any reaction to former Secretary of State Hillary Clinton implying that Congresswoman Tulsi Gabbard might be a Russian asset", Todd said. 'No, I have ruled that out'.
The Daily Beast article said that Gabbard's campaign was being "underwritten by some of the nation's leading Russophiles", and highlighted donations from supporters of Russian President Vladimir Putin.
The Hawaii Army National Guard major went on to accuse Clinton of using her proxies and ties to corrupt media to hurt the Gabbard campaign.
Buttigieg, who like Gabbard has been deployed overseas as part of the military, said it was wrong to "abandon the global stage" or 'think our only choices are between endless war and total isolation'.
She added in a tweet that Clinton has "finally come out from behind the curtain" manipulating the campaign against her through her "powerful allies in the corporate media and war machine, afraid of the threat I pose".