(CNN) A pair of veteran leaders on the left, former Democratic National Committee Chairman Howard Dean and Center for American Progress President Neera Tanden, called on Hawaiians to vote Rep. Tulsi Gabbard out of office after the Democrat questioned whether Syrian President Bashar al-Assad was responsible for last week's chemical attack.

"People of Hawaii's 2nd District -- was it not enough for you that your rep met with a murderous dictator? Will this move you?" Tanden tweeted Friday in response to Gabbard's comments on CNN that she is "skeptical" Assad is responsible for the chemical attack.

People of Hawaii's 2nd district - was it not enough for you that your rep met with a murderous dictator? Will this move you?1 https://t.co/jbwGuZIJ6R

Dean compared Gabbard's comments to President Donald Trump's Twitter blasts.

"This is a disgrace. Gabbard should not be in Congress," the former Vermont governor tweeted. He later added, "She sounds like Trump making excuses."

@CarlNyberg312 @TulsiGabbard Engaging in dialogue isn't the problem. It's claiming there is doubt Assad uses chemical warfare. She sounds like Trump making excuses

Gabbard, who sits on the Armed Services and Foreign Affairs committees, took a somewhat mysterious trip alone earlier this year to meet with Assad in Syria without alerting House Speaker Paul Ryan -- a move that drew scorn from some of her House colleagues. But the liberal Democrat, who was one of then-Democratic presidential candidate Bernie Sanders' few supporters in Congress last year, explained she wanted to engage in dialogue with Assad.

Gabbard told CNN on Friday that she wants to achieve peace in Syria, "Why should we just blindly follow this escalation of a counterproductive regime-change war?"

"There's responsibility that goes around," Gabbard said."Standing here pointing fingers does not accomplish peace for the Syrian people. It will not bring about an end to this war."

Gabbard has also said she is concerned about sparking a nuclear war with Russia, which backs the Assad regime. Tensions between the US and Russia have mounted since the strike, with Russian officials alerting US officials that they were shutting down a line of communication designed to keep Russian and US warplanes from colliding over Syria, although a senior US military official disputed that the communication channel was suspended.

But Secretary of State Rex Tillerson said Sunday that he wanted to be clear the missile strike was a decision solely in retaliation for the chemical attack.

"This strike was related solely to the most recent horrific use of chemical weapons against women, children, and as the President said, even small babies," Tillerson said on ABC's "This Week." "So the strike was a message to Bashar al-Assad that your multiple violations of your agreements at the UN, your agreements under the chemical weapons charter back in 2013, that those would not go without a response in the future. And we are asking Russia to fulfill its commitment, and we're asking and calling on Bashar al-Assad to cease the use of these weapons. Other than that, there is no change to our military posture."

Other liberal lawmakers — including the independent Vermont Sen. Sanders and New York Democratic Sen. Sen. Kirsten Gillibrand — have argued against starting a war with Syria following Thursday's strike, but few have questioned Assad's responsibility for the chemical attack which spurred Trump to action.

Rep. Thomas Massie, a libertarian-leaning Kentucky Republican who frequently sides with the staunchly conservative House Freedom Caucus, also told CNN last week that he was uncertain Assad was behind the chemical attack.

Other mavericks in Congress, including Rep. Walter Jones, a North Carolina Republican who frequently stands alone on issues, have said they want to see more evidence of Assad's involvement — but no one else seems to have gone quite as far as Gabbard.

As of now, it looks highly unlikely that Tanden's recommendation that voters kick Gabbard out of office in 2018 would be successful: Gabbard beat her Republican opponent last November 81%-19%, and she dismissed a Democratic primary challenger 85%-15%.