In endorsing a proposal to eliminate private health insurance plans in favor of government-provided ones this week, Sen. Kamala Harris (D-CA) sparked a debate within her party about both the merits of a single-payer healthcare and the politics of running a campaign on it.

The Medicare for All bill authored by Sen. Bernie Sanders (I-VT) and touted by Harris during a CNN town hall in Iowa on Monday is hardly a secret. It was introduced nearly two years ago and has 16 cosponsors, including many of the senators who are seeking the Democratic presidential nomination or thinking about doing so.

But instead of glossing over one of the main outcomes of creating a single-payer system, Harris said the quiet part out loud. “Let's eliminate all of that,” she told host Jake Tapper, when he asked her about the future of private health insurance plans. “Let's move on.”

The pronouncement was met with nervousness among some Democrats, particularly in the House, where many of the newest members had rejected Medicare for All on the campaign trail in 2018. Democratic Caucus Chair Hakeem Jeffries (D-NY) on Tuesday said it was too early to comment on proposals being floated by presidential candidates, and pivoted to the basic principles on which Democrats were united, like protecting people from pre-existing conditions and lowering prescription drug prices.

“That's our starting point,” he said. “Eventually, I think we all support the concept... that access to high quality, affordable healthcare is a right, it is not a privilege. And we have to make sure that every single American, regardless of zip code, has access to healthcare in America.”

Rep. Max Rose (D-NY), a freshman and a member of the moderate Blue Dog coalition, said he looked forward to the policy debate but said he prefered to fix the current system rather than throwing it out.

“What I think the mistake sometimes that we’re making is, is that we are thinking Medicare for All is a value. Medicare for All is one policy by which we can attain a value, and I look forward to that being the focus of the discussion,” he said. “There are certainly people like myself, that don’t think Medicare for All is the answer.”

While Democrats quibbled over the merits of Medicare for All legislation, Harris’ comments sparked an internal debate over the political vulnerabilities that pushing aggressively for such a bill would bring in the 2020 campaign. Several Democratic operatives, when asked about Harris’s exchange, said that they worried the senator had left herself vulnerable to attacks from Republicans.

“I think the policy is not well defined, leaving it open to unfair GOP attacks on an issue that is easily driven by fear,” said one Democratic strategist. “ I think those supporting it need to do a much better job explaining what they are for, such that they aren’t burdened with false accusations later. Kamala’s issue yesterday is a perfect example.”

For Harris, it was the rare hiccup in a campaign launch that has been widely regarded as a highly successful. The junior senator from California has posted eyebrow-raising fundraising numbers and showcased a digital apparatus that’s impressed her fellow Democrats. But the CNN town hall illustrated a challenge that will confront all 2020 candidates and her in particular. Harris remains a relatively new face on the national political scene, and as she rockets to the head of the 2020 field, she is poised to face a level of scrutiny she has yet to confront.

To date, Harris has yet to truly deal with the onslaught of Trump, his derisive nicknames, or his hate-tweets. A search of past Trump tweets reveals not a single direct mention of the California Democrat. Indeed, while Republicans from the various campaign committees clamoured to attack Harris and Democrats in general after her comments, the president stayed conspicuously silent.

Five Trump associates and aides independently told The Daily Beast that they don’t recall a time when the president complained about or ridiculed Harris during private conversation over the past couple years. He has, however, done so on numerous occasions behind closed doors and in public view about many other liberal figures, and 2020 hopefuls, such as Democratic Sens. Elizabeth Warren (MA), Kirsten Gillibrand (NY), and Cory Booker (NJ). The president has gone after Warren, in particular, in large part because he finds her easy to mock and views her as a useful foil, according to two sources who have talked to him about Warren.

One White House official described Harris as essentially a “non-entity” to Trump—at least “for now.” But others close to the president say that the moment Trump senses that Harris is the frontrunner in the Democratic race, or that she is a clear and present threat to him, he will start going after her regularly. “He won’t keep quiet... for much longer,” a source close to Trump predicted, given Harris’ ascendance in the news cycle and in the pre-2020 spotlight.

However, until then, those around the president currently see no upside to him elevating Harris, and are more than content to let major party organs like the Republican National Committee handle the attacks.

“There’s no reason to elevate a political opponent who’s had an unremarkable start thus far in Washington when elevating established, recycled opponents including former Vice President Biden, Sen. Warren, and Sen. Sanders is a better play,” Jason Miller, Trump’s former communications director for the presidential transition, told The Daily Beast. “One of the major keys to President Trump winning re-election in 2020 is maintaining the ‘change’ label and forcing the eventual Democratic opponent to own the ‘status quo’ description.”

While Harris waits to be on the receiving end of Trump’s ire, she has been bolstered by members of her party’s base. Progressives were thrilled with her Medicare for All answer and praised the momentum her support created.

“Anytime pharmaceutical companies... have to put put tens of billions of dollars into trying to defeat an idea, we know it’s a damn good idea,” Congressional Progressive Caucus Co-Chair Pramila Jayapal (D-WA) told reporters on Thursday.

Jayapal said she planned to introduce Medicare for All legislation in the House next month.

If the debate sounds familiar, it’s because it was the focus of one of the central disputes of the 2016 Democratic primary between former Secretary of Secretary of State Hillary Clinton and Sanders. Clinton criticized the plan as long on cost and short on details. Sanders rejected her criticism as a “Republican argument.”

Sanders legislation would vastly expand Medicare coverage and put an end to copays, deductibles and premiums. The plan, which would be phased in over time, would make the government the sole payer and private insurance would be effectively eliminated.

It’s unclear how the plan would be paid for, though Sanders has suggested a range of ideas, including a payroll tax, an income tax on the wealthy, or taxes on corporations to fit the bill.

While the elevation of the Sanders proposal sets up some potentially uncomfortable exchanges for more moderate Democrats, Harris, for her part is standing firm on her comments even as her aides note she would support more incremental approaches too.

“We support Medicare for All,” said campaign spokesman Ian Sams. “Period.”

—With additional reporting by Sam Brodey and Sam Stein