Mr. Thiel has been an important player in Silicon Valley since the first dot-com boom, but he has recently taken on a much more public role. He was born in Germany and came to the United States as an infant when his father, a chemical engineer, found work here. He was raised in Silicon Valley and went to Stanford, where he developed the views in his first book, “The Diversity Myth,” about the multiculturalism debate on campuses, written with the entrepreneur David O. Sacks.

In 1998, Mr. Thiel helped found the online payments company PayPal, an immediate success. He was the first outside investor in Facebook. Forbes estimates his net worth at $2.7 billion. Last year, he became a part-time partner at Y Combinator, a loosely defined advisory position.

A handful of others in Silicon Valley have similar investing track records. Where Mr. Thiel really separates himself from his peers is his skepticism that Silicon Valley is building a better world for all. His investment firm, Founders Fund, used to begin its online manifesto with the complaint, “We wanted flying cars; instead we got 140 characters,” a reference to Twitter. Now it says simply, “What happened to the future?”

San Francisco, Manhattan and Washington, D.C., are doing well, but the presidential campaign has laid bare the angst of many other places. Feelings of decline are rampant. “Most of the millennials have lower expectations than their baby boomer parents,” Mr. Thiel said. “Where I differ from others in Silicon Valley is in thinking that you can’t fence yourself off. If it continues, it will ultimately be bad for everybody.”

The polls have been saying Mrs. Clinton is likely to win. If that happens, “there will be a very big need to push back on the sort of happy but misleading consensus about things,” Mr. Thiel said. “There will be an important role for me and others to somehow play in speaking truth to power.”

To an extent, that is. “It would be a mistake and inappropriate to instantly demonize Hillary and to try and sabotage her presidency,” he said. That would be repeating what happened in 2008, when the Republican Party did exactly that to President Obama.

That is the larger discussion Mr. Thiel intends to be involved in. Another, more local discussion is already underway about his role in Silicon Valley.