On the state level, ballot measures included a vote on legalization of same-sex marriage by a popular vote and to legalize recreational use of marijuana in Colorado, Oregon and Washington.
Dating back to 1998, same-sex marriage has been rejected in all 32 states that have held popular votes on the issue.
Waiting for results: Christabel Escarez, right, and Daisy Frearson, second from right - both in support of same-sex marriage - watch early election results at the Wildrose bar in Seattle's Capitol Hill neighborhood
Vote: Since 1998, same-sex marriage has been rejected in all 32 states that have held popular votes on the issue, until the streak was broken tonight in Maine
That streak was broken tonight in Maine. Maryland followed suit.
Washington's vote on the subject remains too close to call tonight.
Minnesota voted on whether to place a ban on gay marriage in the state constitution, a divisive issue in that state, where one organization Minnesota for Marriage ran a Facebook photo campaign of Northwestern College students
In the images, students displayed a sign that read 'I'm voting yes because...' with their own personal message.
Backing: Minnesota for Marriage started a Facebook campaign featuring Northwestern College students showing their support for a state ban on same-sex marriages
Divisive issue: In the images, students displayed a sign that read 'I'm voting yes because...' with their own personal message
Three states had the legalization of recreational marijuana on their ballots, measures that would set up a direct challenge to federal drug law. So far, Colorado has voted in favor of it.
Each measure would allow adults to possess small amounts of pot under a regimen of state regulation and taxation.
Passed: Three states had the legalization of recreational marijuana on their ballots, measures that would set up a direct challenge to federal drug law
The Oregon proposal had lagged, but the Washington measure is believed to have a decent chance of passage.
In Massachusetts, voters approved a measure to allow marijuana use for medical reasons, joining 17 other states.
Arkansas voters were deciding on a similar measure that would make it the first Southern state in that group.
A high voter turnout in Puerto Rico took whether to push the territory toward become the 51st U.S. state.
The two-part referendum first asked voters if they wanted to change Puerto Rico's 114-year relationship with the United States.
A second question gave voters three alternatives if they wanted a change: become a U.S. state, gain independence, or have a 'sovereign free association,' a designation that would give more autonomy for the territory of 4 million people.
With 243 of 1,643 precincts reporting late Tuesday, 75,188 voters, or 53 percent, said they did not want to continue under the current political status.
Forty-seven percent, or 67,304 voters, supported the status quo.
On the second question, 65 percent favored statehood, followed by 31 percent for sovereign free association and 4 percent for independence.
'Puerto Rico has to be a state. There is no other option,' said 25-year-old Jerome Lefebre. 'We're doing OK, but we could do better. We would receive more benefits, a lot more financial help.'
To join, or not to join: A high voter turnout in Puerto Rico took whether to push the territory toward become the 51st U.S. state
But 42-year-old Ramon Lopez de Azua said he favored the current system, which grants U.S. citizenship but prevents Puerto Ricans from voting for president unless they live in the United States, and gives those on the island only limited representation in Congress.
He said: 'Puerto Rico's problem is not its political status. I think that the United States is the best country in the world, but I am Puerto Rican first.'
Taking it to the streets: Sixty-five per cent of Puerto Ricans favored statehood, followed by 31 per cent for sovereign free association and 4 per cent for independence
In California, voters were deciding whether to repeal the state's death penalty.
If the measure prevailed, the more than 720 inmates on death row there would have their sentences converted to life in prison.
California voters were also weighing a measure that would require porn actors to wear condoms.
In all, there were 176 measures on the ballots Tuesday in 38 states, according to the Initiative and Referendum Institute at the University of Southern California.
Other notable ballot measures:
- In Oklahoma, voters approved a Republican-backed measure that wipes out all affirmative action programs in state government hiring, education and contracting practices.
Similar steps have been taken previously in Arizona, California, Michigan, Nebraska and Washington.
- Florida voters rejected a proposal that would have banned government mandates for obtaining insurance such as required by President Barack Obama's health care overhaul.
Floridians also rejected a proposed constitutional amendment that would have limited revenue growth to match increases in population and cost of living.