Gregory Korte

USA TODAY

WASHINGTON — In the race for president of the United States, everyone's vote counts. But some count more than others.

That fact of American democracy is never more obvious on Election Day, when the president and vice president are elected state-by-state under systems that change from county-by-county or even precinct-by-precinct.

By the end of the night, more than 100 million individual voting decisions will be distilled into the only votes that count: the 538 votes in the Electoral College. The first candidate to 270 wins.

Beyond the red states and blue states, voters will be segmented into bellwether counties, in-person voters and absentee ballots, and dozens of demographic groups: men and women, the more and less educated, Baby Boomers and Millennials, Catholics and Jews, African-Americans and Hispanics, union and non-union households.

For savvy election watchers, understanding those differences can send signals about who's winning and whose losing even before the last vote is cast. The Associated Press and the television networks have traditionally used exit polling to help quickly "call" states for one side or another. But as more states allow greater access to early voting, it's also possible for significant numbers of votes — more than half in some states — to be counted and reported immediately after the polls close.

What time do polls open and close in each state on Election Day?

With the results in most states seemingly predetermined, the race comes down to a handful of "swing states" — places like Florida, North Carolina, Ohio and Nevada. Most analysts agree that Donald Trump needs more of those states than Hillary Clinton does.

But the president isn't the only federal office on the ballot. The 2010 Tea Party surge swept in a class of Republican senators now defending their seats. Twenty-four of the 34 Senate seats are being defended by Republicans, and Democrats only need to win five of them to regain control of the Senate — or just four if Democratic vice presidential nominee Tim Kaine is presiding.

Here's a guide to watching the returns:

5 a.m. ET

Every state has different poll opening and closing times, but in Vermont the polls can open as early as 5 a.m. And almost as soon as poll workers show up, there will almost certainly be problems reported.

Locked polling places. Long lines. Power outages. Ballot shortages. Those are all problems that can bedevil election officials even in a less contentious election year. Social media and growing distrust of the election system will shine a brighter light on them this year.

And given the acrimony of 2016 — and Trump's charges that the election will be "rigged" — both sides will be carefully watching to make sure elections are conducted peacefully and fairly.

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6 p.m. ET

Polls close in most of Indiana and Kentucky.

Senate race to watch: Democratic hopes to win the Senate could depend on a comeback by Democratic former senator Evan Bayh, scion of an Indiana political family. Bayh has been in a tight race with GOP Rep. Todd Young for the seat now occupied by retiring Sen. Dan Coats.

7 p.m. ET

Polls close in Georgia, South Carolina, Vermont and Virginia, most of Florida, and the western parts of Indiana and Kentucky.

Battlegrounds: Florida is one of the first states with polls to close, and — if recent elections are any guide — will be one of the last states to be called. That means election watchers could have one eye on the Sunshine State for much of the night.

But early voting could give some early indications: As of Sunday, 6.2 million voters had already cast ballots. That's nearly half the number of registered voters, and three-quarters of the number voting in 2012. Registered Democrats had cast 32,528 more votes than registered Republicans, but that gap is narrower than it was in 2012.

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Hillsborough County, home of Tampa, has the ethnic and economic diversity to make it a near-perfect microcosm, with a mix of longtime residents and snowbirds from other swing states like Michigan and Ohio. “That diversity in geography and diversity in demographics makes Hillsborough County such a purple county," said Ana Cruz, the former head of the Florida Democratic Party. Hillsborough is "a microcosm of what this battleground state of Florida represents."

By all rights, Georgia shouldn't be in play; it hasn't gone Democratic since Bill Clinton in 1992. Trump has a healthy lead in recent polls, so a Clinton win — or even a close race — could signal trouble for Trump later on. One reason: It would likely signal a motivated African-American turnout, which is going overwhelmingly for Clinton.

7:30 p.m. ET

Polls close in North Carolina, Ohio and West Virginia.

Battlegrounds: Ohio, Ohio, Ohio. It's not as important as it was a decade ago, but it's still more important to Trump as it is to Clinton. No Republican has won the White House without it. And on paper, it should be fertile ground for Trump's message: It has a high proportion of white voters without a college degree, and it's been buffeted by job losses caused by globalization.

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Look to swing counties like Stark, Ross and Clark as bellwethers. Ottawa County, on Lake Erie, has predicted the national winner every year since 1964. But don't call the state until Cleveland vote comes in. Cuyahoga County often reports its votes late, and its high concentration of true-blue Democratic voters can cancel out Trump wins downstate.

"I always feel like the Republican generally leads in the middle portion of the night, and then we wait and see if what happens in Cuyahoga," said Kyle Kondik, author of The Bellwether: Why Ohio Picks the President.

North Carolina is enjoying — if that's the right word — its newfound status as a swing state. In 2008, President Obama was the first Democrat to win it since 1976, but he lost it to Republican Mitt Romney four years later. It's gotten plenty of attention from both campaigns — and from Obama, who made three stops there in the last week of the campaign.

At the same time, the state has been roiled by debates on transgender bathrooms and voting rights.

The African-American turnout was key to Obama's 2008 victory and is crucial for Clinton as well. "If she doesn’t have a decent showing by black voters, then it makes it that much harder to make the state flip to blue," said Mike Bitzer, a political scientist at Catawba College. Early voting is a good sign of whether the Clinton campaign has been successful in getting those voters to the polls; the first returns reported after the polls close could be revealing.

Senate race to watch: Democrat Deborah Ross, an American Civil Liberties Union lawyer, is challenging Republican Sen. Richard Burr in the Tar Heel State. Burr made national headlines in the final days with comments about putting a bull's-eye on Clinton and promising to block Supreme Court nominees for another four years.

8 p.m. ET

Polls close in Alabama, Connecticut, Delaware, the District of Columbia, Illinois, most of Kansas, Maine, Maryland, Massachusetts, most of Michigan, Mississippi, Missouri, New Hampshire, New Jersey, Oklahoma, Pennsylvania and Rhode Island, most of Texas, eastern Tennessee and the Florida panhandle.

Battlegrounds: Pennsylvania is so important to Democrats that Clinton decided to end her campaign there with a Philadelphia rally that brought her heaviest hitters — the president and first lady — back to the city where she was nominated. A big turnout in Pennsylvania is essential for her, but much of the attention will be in the suburban "collar counties": Bucks, Chester, Delaware and Montgomery. The moderate Republican voters there are usually a counterbalance to the urban Democrats, but this year could be different.

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"In Donald Trump, you have a perfect storm of a candidate in terms of pressing buttons to sending white, college-educated voters, particularly women, in the other direction," said Ruy Teixeira, a fellow at the liberal Center for American Progress.

Part of Michigan's Upper Peninsula is on Central time, so polls there close an hour later. But networks could call the state earlier based on exit polls in the Eastern time zone. Turnout in Detroit's Wayne County will be a key indicator of Clinton's support among African-Americans, but a better bellwether might be Macomb County, just north of 8 Mile Road. It's historically been ground zero for Reagan Democrats and could indicate whether Trump's anti-trade, anti-immigration message swings enough union members to close the gap.

Trump, Clinton each face challenges courting African-American vote in Detroit

Maine is a curiosity, because it's one of two states (Nebraska is the other) that splits its electoral votes by congressional district — giving Trump a chance to pick up a spare vote in Maine's 2nd district.

New Hampshire voters have seen these candidates up close more than anyone else, and Trump has surged in the polls there in recent weeks. A Trump win may not be decisive — it has just four electoral votes — but it could be a signal of whether Trump's rebound is for real.

Senate races to watch: In Missouri, GOP Sen. Roy Blunt faces a surprisingly strong challenger in Democratic Army veteran Jason Kander. In New Hampshire, Democratic Gov. Maggie Hassan is taking on GOP Sen. Kelly Ayotte in a race dominated by the candidates' relationship to the presidential candidates. And in Pennsylvania, Republican Sen. Pat Toomey is fending off a challenge from Katie McGinty, a former environmental protection official with close ties to Clinton and Obama.

8:30 p.m. ET

Polls close in Arkansas.

9 p.m. ET

Polls close in Arizona, Colorado, western Kansas, Louisiana, the western Upper Peninsula of Michigan, Minnesota, eastern Nebraska, New Mexico, New York, western South Dakota the western panhandle of Texas, Wisconsin and Wyoming.

Battlegrounds: In a normal election year, Arizona would be safely in the Republican column. The state has gone Democratic just once since 1948, and that was in the three-way race in 1996 when Reform Party candidate Ross Perot siphoned off Republican votes. While an Arizona Republic poll three weeks ago showed Clinton up by 5 percentage points, more recent polls have favored Trump.

But those poll results are based largely on models that show that Hispanic voters are historically underrepresented in voter turnout. And Democrats are hoping that Trump's anti-immigration rhetoric will drive Latinos to the polls. Exit polls will show whether that's happening.

Obama carried Colorado twice, moving it from purple to blue on most electoral maps, and Clinton leads in most recent polls. And its demographics work against Trump: It's younger, more educated and more Hispanic than the country at large.

But Trump visited the state Saturday night, and GOP officials say they've pulled ahead on mail-in votes submitted by Republican voters.

"I don't think people are talking about it today, but we're 1,700 votes ahead in an all mail-in state in Colorado today. It is a jump ball in Colorado," Republican National Committee Chairman Reince Priebus said on ABC's This Week.

That's a change from a week ago, when Trump visited the state and claimed there were "real problems with ballots being sent" and encouraged supporters to vote in person.

In New Mexico, Clinton has had a consistent lead in the polls, with the latest Albuquerque Journal poll showing her leading, 45% to 40%. So the most interesting thing to watch may be how well former New Mexico governor Gary Johnson does. The Libertarian candidate once hoped to play spoiler here, but his support has been cut to 11% from his high-water mark of 24% in September.

10 p.m. ET

Polls close in southern Idaho, Iowa, Montana, Nevada, eastern North Dakota, far eastern Oregon and Utah.

Battlegrounds: Once considered competitive, Iowa seems to be trending in Trump's direction. A Des Moines Register poll published Sunday showed him up by 7 percentage points.

“The bigger surprise on election night would be if he lost Iowa, not that he won it,” said Amy Walter, national editor at the nonpartisan Cook Political Report. “Donald Trump can’t afford to lose Iowa, and Hillary Clinton can.”

Like Colorado, Nevada is another state where the two main sources of predictive data — polls and early votes — are trending in opposite directions. Trump seems to have a slight lead in recent polls, but a surge of early ballots cast by registered Democrats would seem to favor Clinton.

Trump needs crossover and independent votes — and big turnout by Republicans on Election Day — to overcome a 40,000-ballot early-vote advantage by registered Democrats.

But Rep. Mark Amodei, R-Nev., told a Trump rally in Reno on Saturday that the early voting numbers fail to take into account independent voters, who he said will break toward Trump on Tuesday. “Guess what, the history in Nevada is Election Day is elephant day. Election Day is independent day," he said.

Also closely watched will be the fate of Utah's six electoral votes, with recent polls showing insurgent conservative Evan McMullin within striking distance of Donald Trump. McMullin would be the first third-party candidate to win electoral votes since George Wallace in 1968 — and those are electoral votes Trump needs.

Senate race to watch: The retirement of Senate Minority Leader Harry Reid leaves an open seat in Nevada. Hoping to fill it are Catherine Cortez Masto, the Democratic former state attorney general, and GOP Rep. Joe Heck.

11 p.m. ET

Polls close in California, Hawaii, northern Idaho, western North Dakota, most of Oregon and Washington.

12 midnight ET

Polls close in most of Alaska.

1 a.m. ET

Polls close in half the Aleutian Islands of Alaska.

Contributing: Joel Burgess of the Asheville Citizen-Times, Susan Page of USA TODAY, Alexandra Glorioso of the Naples Daily News, and Amy Bennett Williams of the Fort Myers News-Press, Jason Noble of the Des Moines Register, Seth Richardson of the Reno Gazette-Journal.

More election coverage from USA TODAY:

• Plot Trump's or Clinton's path to 270 electoral votes

• See the latest national and state presidential polling averages

• Check out poll closing times in each state

• Candidate info and ratings for all races