Ed Rendell, former Pennsylvania governor and Democratic National Committee chairman, threw a glass of ice-cold water on Donald Trump's attack on Hillary Clinton.
Trump on Wednesday lashed out at the presumptive Democratic nominee, saying she was a "world class liar" and alleged that she used the State Department as her "own personal hedge fund."
Rendell, a frequent Clinton surrogate, said voters are unlikely to be swayed.
"[For Trump] to say Hillary Clinton's against the LGBT community, to say Hillary Clinton's against African-Americans, you might as well try to convince people that Hillary Clinton's a vampire. I mean, it's just not going to work," Rendell told CNBC's "Squawk Alley."
And while Trump cited few sources in his attacks on Clinton, Rendell said the former secretary of state was taking a different approach.
"Hillary Clinton has used, specifically, quotes from Donald Trump himself, and every quote is backed up with a citation. So these are Trump's words that she's using to categorize Trump himself," he said.
In Trump's speech, he said he would lower taxes and "build the greatest infrastructure on planet Earth" among other things. Rendell said those promises might be hard to keep.
"You don't lower taxes, and then get money to fund a massive infrastructure and redevelopment program. So of course Donald Trump hasn't told us how he would fund that all," he said.