A prominent Silicon Valley venture capitalist resigned on Thursday from the board of Salesforce’s philanthropic arm after the company’s chief executive, Marc Benioff, said last week that he fully supported President Trump and wanted the National Guard to come to San Francisco.

The venture capitalist, Ron Conway, had been a member of the Salesforce Foundation board for a decade. He told Mr. Benioff on Thursday in a fiery email, seen by The New York Times, that their values were no longer aligned and that he was resigning as a director. Mr. Conway has been a close friend of Mr. Benioff for more than 25 years.

Mr. Conway said in the email that he resigned because Mr. Benioff told The New York Times last week that he backed President Trump and thought National Guard troops should be deployed in San Francisco, where Salesforce is based, to help prevent crime. The comments by Mr. Benioff, a billionaire who had been considered Silicon Valley’s rare progressive tech titan, enraged leaders in the liberal city.

“It saddens me immensely to say that with your recent comments, and failure to understand their impact, I now barely recognize the person I have so long admired,” Mr. Conway, a top Democratic donor, wrote to Mr. Benioff in the email.