This summer, the world’s first trillionaire and this year’s biggest campaign donor was asked about his inordinate economic and political sway in the United States.

“Is this different from the past?” Elon Musk answered during an interview with Britain-based The Economist.

It’s a startling question, one that sits uneasily for a nation whose Constitution states that all men are created equal and whose government is supposed to be “of the people, by the people, and for the people,” as President Abraham Lincoln put it.

In a sense, Mr. Musk is right. Big money has long influenced American politics.

But there are also big differences between the Gilded Age tycoons and the Silicon Valley tech titans of today, historians say.

“The most important difference between then and now is that campaigns now are infinitely more expensive than they have ever been,” says David Nasaw, history professor emeritus at CUNY Graduate Center and author of a biography on industrialist Andrew Carnegie.…