Hewlett-Packard CEO Meg Whitman hit the campaign trail Tuesday for Hillary Clinton, making the business executive the first Republican to stump for the Democratic nominee.

Whitman, who has voted Republican her entire life, appeared at a campaign event in Denver, Colo., with business leaders from around the Centennial State.

"I'm a lifelong Republican but this year I'm supporting Hillary Clinton," Whitman reportedly told her audience. "I'm not just supporting [Hillary Clinton], I'm all in."

"The stakes in this election are significant. We have to put country before party," she said.

The Democratic nominee has "compassion, commitment and courage," the business CEO said, adding that Clinton would be excellent for the U.S. economy.

"If you are a lifelong Republican, it's hard to come across [the partisan divide,]" Whitman said, according to the Denver Post. "But I decided that this year it was clear to me that Secretary Clinton's temperament, leadership experience and commitment to America's foundational values make her the far better choice for president."

Later, in an interview with a local NBC News affiliate, she hinted that she was open to the idea of serving in the Clinton administration if asked.

"We'll see what happens," Whitman said.

Whitman's visit to Colorado comes shortly after she announced this month that she couldn't vote for GOP nominee Donald Trump.

"To vote Republican out of party loyalty alone would be to endorse a candidacy that I believe has exploited anger, grievance, xenophobia and racial division," she wrote in an essay titled "Who I'm Voting for and Why." "Donald Trump's demagoguery has undermined the fabric of our national character."

She accused Trump of being "reckless" and "uninformed" on an array of issues, including immigration and foreign policy.

"Therefore, I have decided to support Hillary Rodham Clinton. It is clear to me that Secretary Clinton's temperament, global experience and commitment to America's bedrock national values make her the far better choice in 2016 for President of the United States," she wrote.

"In a tumultuous world, America needs the kind of stable and aspirational leadership Secretary Clinton can provide. I urge all Republicans to reject Donald Trump this November," she added.

Trump's team has responded Whitman's campaigning for Clinton by knocking the business CEO for her failed 2010 California gubernatorial bid.

"It's incredibly disappointing, but it's more disappointing than surprising," said the GOP nominee's campaign manager, Kellyanne Conway. "Let's remember: Meg Whitman lost her own race by 12 points."

Whitman lost by 13 points.

"It tells you something that people who run as Republicans but don't run as conservative Republicans and try to show a contrast and her opponent at the time, Barbara Boxer as I recall, they lose," she said.

Whitman didn't run against Sen. Boxer. She ran against California Gov. Jerry Brown.