More than 50 business executives, including several longtime Republicans, endorsed Hillary Clinton for president on Thursday as her campaign seeks to capitalize on discomfort with Republican Donald Trump.

They include Jim Cicconi, senior executive vice president at AT&T Services Inc., and Dan Akerson, who held top positions at General Motors Co. and Nextel Communications Inc. A Clinton campaign aide provided the list.

The endorsements reflect continuing unease among some Republicans with the presumptive Republican presidential nominee despite his romp through the primary contest.

Mr. Cicconi, who worked in the White House for Presidents Ronald Reagan and George H.W. Bush, said he has backed every GOP presidential candidate since 1976. “But this year I think it’s vital to put our country’s well being ahead of party,” he said in a statement provided by the campaign. “Hillary Clinton is experienced, qualified, and will make a fine president. The alternative, I fear, would set our nation on a very dark path.”

Mr. Akerson said he has consistently voted for Republicans for president in the past but couldn’t support Mr. Trump. “Serving as the leader of the free world requires effective leadership, sound judgment, a steady hand and most importantly, the temperament to deal with crises large and small. Donald Trump lacks each of these characteristics,” Mr. Akerson, who also served as a Navy surface warfare officer, said in a statement provided by the campaign.