COLORADO SPRINGS — Days after Bernie Sanders officially backed a ballot measure in Colorado that would create the first universal healthcare system in the nation, the Green Party’s presidential nominee, Jill Stein, said she is not ready to endorse the plan.

“I don’t want to throw my weight behind an endorsement at this point,” Stein told The Colorado Independent in a sit-down interview before a packed speech at a downtown Unitarian Universalist church. “But I would certainly respect anyone who sees fit to work on it.”

Stein said she supports a “complete single-payer program” at the federal level.

The physician from Massachusetts is in Colorado for the day on a campaign swing along the Front Range.

ColoradoCare, she said, has important principles and has inspired voters to mobilize in Colorado, which underscores the need for what she called “comprehensive and secure” healthcare. But she said she has concerns about gaps and loopholes in the measure— she did not specify what they are— and has questions about whether those shortcomings could be “filled in.”

In Colorado, the measure has divided Democrats. The state’s leading progressive group, ProgressNow, recently came out against it, and the state’s Democratic establishment have largely panned the proposal. Some worry about large new taxes, while others, like the pro-choice NARAL of Colorado, have concerns the plan would restrict abortion access.

Related: Sen. Irene Aguilar discusses ColoradoCare’s terrible, horrible, no-good, very bad week

Asked if she would urge her supporters in Colorado to vote for the measure, which will be on the ballot in November, Stein said she would leave it up to them.

“I know our supporters are actually split,” she said. “And there are many who have been very involved intensively and there are others who praise the movement but who aren’t actively involved.”

In October, Sanders told The Colorado Independent in a statement he believed the state could “lead the nation” by passing ColoradoCare. But he officially endorsed the measure this week through his new group Our Revolution.

In Colorado, Stein’s supporters who met her at a downtown park and marched with her through the downtown streets to the church, loudly criticized Democratic presidential nominee Hillary Clinton more than Donald Trump.

“Hell no to DNC, we won’t vote for Hillary,” they chanted at times.

Stein has about 7 percent support in Colorado, a state with about 10,000 registered Greens, according to a recent Quinnipiac poll, and she is likely angling for the votes of disaffected supporters of Bernie Sanders, who beat Clinton by 19 points in the March 1 caucuses here.

But Stein’s non-endorsement for the ColoradoCare measure puts her at odds with the Green Party’s U.S. Senate nominee in Colorado, Arn Menconi, a full-throated supporter of the measure, which is also called Amendment 69.

“People want her to take a leadership role on Amendment 69,” Menconi said of Stein outside the church, following the Stein speech. Menconi said while leadership in the state Green Party is not fully supportive of the measure, most members he has spoken with throughout his campaign are and he hans’t heard anyone but a state co-chair for the party raise concerns about the plan.

Both Menconi’s major-party opponents in the U.S. Senate race, incumbent Democrat Michael Bennet and Republican Darryl Glenn, oppose ColoradoCare. Libertarian nominee Lilly Tang Williams is also against it.

Menconi said he would work on Stein throughout her campaign visit to Colorado.

“I’ll bet you we’ll see a change in 48 hours,” he said.

UPDATE: Stein later appeared in Denver, where she addressed the ColoradoCare ballot measure to a crowd at the beginning of a speech.

“It’s so awesome to be here in Colorado where you are leading the charge in so many ways starting with marijuana legalization … and now on this Amendment 69 you are moving us forward … and by the way Amendment 69 shows why we also need improved Medicare for all at the national level,” Stein said. “Because we need the enabling legislation at the national level in order to make it possible to really have the streamlined merger into a single-payer system. Ultimately that’s where we want to go, but measure 69 gets us started and that’s critical. Thank you for leading the way.”

She also called for an improved Medicare-for-all system at the national level, adding, “We support what Colorado is doing with Amendment 69 to get us along that pathway.”