Abolition wasn’t even part of his original plan. He thought, as many people did at the time, that the Electoral College needed only a few tweaks. As chairman of the Senate’s subcommittee on constitutional amendments, Mr. Bayh arranged for hearings on various reform proposals. On the first day of hearings, he rejected the idea of a national popular vote out of hand. The smaller states, which believed they benefited from their disproportionate number of electoral votes, would never go for it. “Putting it optimistically,” he said, the chances of Congress passing a popular-vote amendment were “extremely slim, if not hopeless.”

A few months later, he did a complete about-face.

In a remarkable speech on May 18, 1966, Mr. Bayh said the hearings had convinced him that the Electoral College was no longer compatible with the values of American democracy, if it had ever been. The founders who created it excluded everyone other than landowning white men from voting. But virtually every development in the two centuries since — giving the vote to African-Americans and women, switching to popular elections of senators and the establishment of the one-person-one-vote principle, to name a few — had moved the country in the opposite direction.

Adopting a direct vote for president was the “logical, realistic and proper continuation of this nation’s tradition and history — a tradition of continuous expansion of the franchise and equality in voting,” he said.

He then explained how the Electoral College was continuing to harm the country. The winner-take-all method of allocating electors — used by every state at the time, and by all but two today — doesn’t simply risk putting the popular-vote loser in the White House. It also encourages candidates to concentrate their campaigns in a small number of battleground states and ignore a vast majority of Americans. It was no way to run a modern democracy.

In short, Senator Bayh said, the president “should be elected directly by the people, for it is the people of the United States to whom he is responsible.”

The speech was galvanizing, and by 1968, his popular-vote campaign had won the support of 80 percent of the country, according to a Gallup poll — Republicans and Democrats, as well as organizations as varied as the Chamber of Commerce, the League of Women Voters and the American Bar Association.

Then came the chaotic election of 1968, when George Wallace, the former Alabama governor and arch-segregationist, nearly managed to deadlock the vote and force Congress to pick the winner. Most people were just beginning to understand how bizarre and dangerous the Electoral College was. The prospect of an unreconstructed racist determining the presidency rightly horrified them. As the best-selling author James Michener wrote in a book advocating a switch to the popular vote, the Electoral College was a “time bomb lodged near the heart of the nation.”