Democratic energy 'very high' but 'that does not mean we let up': Jennifer Granholm

CHICAGO -- Former Michigan Democratic Gov. Jennifer Granholm praised the party's energy at its national convention in Chicago as Vice President Kamala Harris prepares to formally accept its presidential nomination.

"It is very high," Granholm told ABC News about Democrats' enthusiasm. "People will be exhausted if it stays this high all the way through. But honestly, for Democrats, it has to stay high. There is so much work to do if we can't take anything for granted. These polls are starting to look good. It's clear she's got momentum, but this is not for time to let up on the accelerator."

Still, Granholm said, it's hard to take anything for granted.

Trump remains the leader of his own movement of loyal supporters, and polling in the past has consistently underestimated his support, including in 2016, when he overcame historical trends and his own stumbles to beat former Secretary of State Hillary Clinton, who Democrats were virtually certain would prevail.

"Always concerned about overconfidence. You always have to run like her 10 points behind. Yes, she's got momentum, but that does not mean you let up, you accelerate. Let's keep going," she said.

Still, Granholm said, Democrats are putting forth an inspiring candidate.

Harris would be a groundbreaking president as a woman of color. But, Democrats have argued, her appeal expands beyond that.

"I do think that it is emblematic of the diversity and coalition that the Democratic Party represents," Granholm said. But her policies "are what really gets and bring people in, in addition to the more than symbolism of having a first in a woman person of color."

Harris is set to blitz the campaign trail in the sprint to Election Day on Nov. 5, even making a pit stop in Milwaukee, Wis., on Tuesday night while the convention plays out in Chicago.

And, Granholm said, it would behoove Harris to have President Joe Biden tag along and allow him to talk about accomplishments that voters may not be aware of, including investments in infrastructure and science and technology.

"What he's done is given her a foundation on which to build," she said.

"He's also somebody who has been focused on bipartisanship, so independents and others who may not be aware of what this president has done and be able to help get the word out, for some weirdo reason, people still seem to think that Republicans have a better agenda, when, in fact, for real people, the agenda that the Democrats are putting forward is so much better, he can be a great explainer for that," she said.