The activism of the era made it easy to mobilize liberals and students, many of whom were already involved in the antiwar and civil rights movements. “People were pretty revved up during that time to get involved in something,” said Mr. DuPell, who started the New Jersey campaign and recruited Mr. Goldstein and Mr. Norbe to join him. But campus unrest and violent protests helped fuel pushback that they were too immature to vote.

“It was kind of an uphill battle for us trying to convince people young people were responsible, because it was an era when, from a national political point of view, the national leaders were pitting young against old,” Mr. Goldstein, now 68, said. “Our thing was, ‘We’re going to try and work within the system.’ There was all this tumult going on across the country. We didn’t think that would help us convince people that they should lower the voting age.”

In April 1969, the Republican-led New Jersey Legislature approved a state constitutional amendment to lower the voting age to 18. And when summer came, Mr. DuPell, Mr. Goldstein and Mr. Norbe went home to build their organization — they called it the Voting Age Coalition Inc. of New Jersey — and round up support for the voter referendum needed to ratify the amendment.

They appointed county leaders, who appointed municipal leaders. They sold membership cards for a dollar and told the buyers to recruit 10 volunteers apiece. When President Nixon came to campaign for William Cahill, who was eventually elected governor, Mr. Goldstein and Mr. DuPell forged press credentials and sneaked into the rally with a sign seeking Nixon’s endorsement. Mr. Goldstein recalled that Secret Service agents carried him out, but their sign ended up in a front-page photo the next day.

Similar efforts were bubbling up in other states. Sometime in the spring, a group of students in Ohio contacted the New Jerseyans and asked if they, too, could use the “Voting Age Coalition” name. By January 1970, students in 13 states were organizing to lower the voting age.

Voters in New Jersey rejected their amendment, and the Voting Age Coalition started trying to lower the age to 19 instead. But it soon became clear that the momentum in Washington, driven by the combined force of the states, was building faster.