(Reuters) - Hewlett Packard Enterprise Co chief executive and Republican donor Meg Whitman reiterated her opposition to Donald Trump as the party’s presidential nominee and compared him to fascist leaders Adolf Hitler and Benito Mussolini, according to media and two sources.

Meg Whitman, Chief Executive Officer of Hewlett-Packard gives an interview to CNBC on the floor of the New York Stock Exchange November 2, 2015. REUTERS/Brendan McDermid

Whitman made the comment Friday at a conference hosted by previous Republican nominee Mitt Romney, while she challenged U.S. Speaker of the House of Representatives Paul Ryan on his endorsement of Trump, the Washington Post reported on Saturday.

Two participants at the off-the-record session in Park City, Utah confirmed Whitman’s language to Reuters. Whitman could not immediately be reached for comment.

A billionaire and former supporter of failed candidate New Jersey Governor Chris Christie, Whitman has been actively working to stop Trump’s nomination, including fundraising for an anti-Trump Super PAC.

In February, the technology CEO called Trump “unfit” to be president. Since then, Trump has become the presumptive Republican nominee and is likely to run against Democratic candidate Hillary Clinton in the Nov. 8 election.

Ryan, addressing the 300 attendees of the session, explained the difficulty he had with the decision to endorse, the Post said, including weathering pressure from House Republicans to lend his backing to Trump.

After weeks of holding out, Ryan endorsed the New York businessman in early June, breaking with a number of establishment Republicans who see Trump’s rhetoric as damaging to the party. The opponents include Romney, Republicans’ 2012 presidential nominee, who chose Ryan as his running mate.

Romney has blasted Trump in recent weeks for attacks he has made on the Mexican-American judge presiding over a case against him, with Romney warning on Friday about the effect that “trickle-down racism” could have on the country.

As the presumptive nominee, Trump now has to balance maintaining the outsider style that helped propel him to the nomination, while courting Republican insiders, who could be critical to financing a general election campaign against a well-funded Clinton.

Trump on Saturday showed no inclination to make peace with his critics. He went on Twitter to note how Romney “choked like a dog” when he lost to then-incumbent President Barack Obama in 2012 and reiterated it at his campaign stops.