Hillary Clinton’s campaign would like to turn the drip-drip-drip of Republican defectors abandoning Donald J. Trump into a deluge.

On Wednesday, after days in which several high-profile Republicans said they could not support Mr. Trump or were endorsing Mrs. Clinton, her campaign introduced an official outreach effort to target Republicans, along with a list of nearly 50 Republican and independent former cabinet secretaries, House and Senate members, ambassadors, national security leaders and business executives who are supporting Mrs. Clinton.

The group, called Together for America, includes the prominent George W. Bush administration official Carlos M. Gutierrez, a businessman and former secretary of commerce; former Representative Connie Morella, of Maryland; and John D. Negroponte, the former director of national intelligence in the Bush administration.

The list also includes previously announced supporters, including Meg Whitman, the California Republican fund-raiser and technology executive.