NATIONAL NEWS (CNN) — A long and bitter presidential election comes to a close Tuesday when Americans choose between a second term for President Barack Obama and a new direction with former Massachusetts Gov. Mitt Romney.
CNN's reporters, correspondents, analysts and anchors share what they'll be watching for that might tip off how the election will go:
CNN Senior Congressional Correspondent Dana Bash: Unexpected GOP struggles in Senate
The neck-and-neck presidential race might be dominating headlines, but there are a lot of rich dramas playing out across the country in the battle for control of the Senate.
Heading into Election Day, there are nearly a dozen true toss-up races that could go either way.
Republicans hold 47 seats. To retake control of the Senate, the GOP needs a net gain of four. With 23 Democratic seats up for grabs in a terrible economy, it seemed like a no-brainer that Republicans would be able to flip four. But it's now a struggle for the GOP.
The central reason is that they are defending several unexpected races on their own turf. Indiana's Senate race is now going to be one of the evening's early bellwethers to determine the balance of power in the Senate. GOP candidate Richard Mourdock's poll numbers plummeted in this red state after he awkwardly stated a few weeks ago that pregnancy from rape is a gift from God. Polls close at 7 p.m. ET, and if Democrat Joe Donnelly wins, it will set Republicans back -- especially since the GOP already expects to lose the seat vacated by retiring Sen. Olympia Snowe in Maine. The state's popular former governor, independent candidate Angus King, is on track to win there.
Here are three other nail-biters I'll be watching:
Virginia: With more than $80 million spent so far, it's the most expensive Senate race in the country. Former GOP Sen. George Allen is trying to get his seat back after a narrow defeat six years ago. The man who beat him, Jim Webb, is retiring and former governor and DNC chairman Tim Kaine hopes to keep the seat in Democratic hands.
Montana: Neither Republicans nor Democrats will even privately predict which way this will go. Incumbent Democrat Jon Tester is trying to hold on for a second term in this red state. GOP challenger Rep. Denny Rehberg started out the race about 1% ahead in the polls. Now, $50 million later, they're in the exact same place -- a 1% differential between them.
Massachusetts: Going into Election Day, Republican strategists were pessimistic about holding onto this red seat in the traditionally blue state. GOP Sen. Scott Brown had fallen behind his well-funded Democratic challenger, Elizabeth Warren -- a liberal icon who served as the president's former consumer advocate.
Brown's win in the race to fill the late Ted Kennedy's seat stunned the political world, and he insists he'll surprise everyone again. But the president is expected to take Massachusetts by double digits -- and with him at the top of the ticket, it may be hard for Brown to beat back a Warren win.
CNN Chief Political Analyst Gloria Borger: How will the white vs. nonwhite vote split
One important indicator I will be looking at Election Night is the question of ethnicity -- and how the white vs. the nonwhite population splits. In the 2008 election, 74% of the electorate was white. That percentage has declined recently because of the growth in the Hispanic and voting African-American population.
Given the ongoing Republican trouble with Hispanic voters and the assumption that African-Americans will, once again, vote overwhelmingly for the president, Mitt Romney needs a strong white turnout to help propel him to victory.
In an analysis by Republican pollster Bill McInturff, the question of the white/nonwhite divide is called the most "critical" of the election. His analysis shows that if the white percentage of the electorate drops to 72%, Obama will probably win the election.
One key to watch is how the white vote itself splits between Obama and Romney.
In the latest national poll CNN/ORC International, taken from Friday to Sunday, Obama received 40% of the white vote while Romney got 57%. In 2008, Obama received 43% of the white vote, which means he is polling less than that currently.
CNN Chief Political Correspondent Candy Crowley: Virginia suburbs and I-4 corridor
The first thing I'll watch is the exit polls to see who's voting and where -- in particular, heavy Latino turnout in Colorado, Nevada, Virginia and Florida could indicate Obama wins those states.
Then, it's Virginia, Florida and Ohio.
I'll watch the Virginia suburbs of Washington, particularly the female vote. Romney won't win here, but he has to hold down Obama's numbers while running up his own score in the rural area. Romney has to win Virginia.
Florida is all about the Interstate 4 corridor. North of it votes Republican; south of it votes Democratic. The I-4 corridor decides.
Everyone will tell you to watch Lake, Stark and Hamilton counties in Ohio. There are good reasons to watch all of them, reasons no doubt delineated by my colleagues. But for me, it's all about Ottawa County, which has correctly picked the presidential winner in Ohio since 1944. That's a better record than pollsters. I'll watch Ottawa.
CNN Political Reporter Peter Hamby: How goes Pasco?
Polls begin to close in Florida at 7 p.m. ET, and a handful of counties will report their absentee and early vote tallies immediately.
Once that happens, political pros in Florida will be anxiously refreshing election board websites in a handful of those counties -- Pinellas, Duval, Orange -- in search of early clues about which way the state is trending.
One of them is Pasco County, outside of Tampa. Officials there are diligent about posting returns as quickly as possible. The county has a slight Republican tilt, but Obama won the early and absentee vote there in 2008 despite losing the county on election night. For Democrats, it was a promising sign that Obama was well on his way to being competitive statewide, even in GOP-leaning areas.
In 2004, George W. Bush beat John Kerry in the Pasco early/absentee vote by 8 points. Bush ended up winning the county by 10 points. In a shift four years later, Obama beat John McCain by 5 points in the early absentee vote. He ultimately lost the county -- but only by 3.5 points, thanks to the votes the campaign banked early.
If Obama is losing Pasco by more than that Bush/Kerry margin by the time the first returns are posted, it could be a tough night for Obama in Florida.
"If you are looking for good news for Romney out of Pasco, if they have a 10- to 12-point lead in the absentee and early vote, that probably portends that they are going to have a really good night in suburban counties," said one top Florida Democrat.
CNN Chief National Correspondent John King: The suburban vote and who votes in the swing states
A narrow and then a more global point:
-- Watch the vote in the suburbs around Cleveland and Columbus, Ohio, and in northern Virginia. These are two early-closing states; if Romney is holding his own in the suburbs, we have a competitive night. If not, it could be effectively over before we get to the Central Time zone.
-- Who votes determines who wins: The composition of the electorate in the swing states is the first and best clue. Does the electorate look like 2008?
If so, then Obama is likely on a path to victory. But if the percentage of African-American, Latino and younger voters is down just a bit -- and the electorate looks, say, more like the 2004 presidential election -- then Romney has a shot.
CNN Political Director Mark Preston: What happens afterward?
It goes without saying that we are all looking at turnout in the key battleground states -- can Romney and Obama get their respective bases to show up at the polls and at the same time, convincing the independent voters to vote for them today?
What is piquing my interest is not only what happens in the next few hours but what will be the political climate for the next president-elect. Washington is already polarized and there are great challenges facing Congress before the end of the year.
Whoever wins the presidency and the parties that control the House and the Senate need to put the bitterness of this election behind them and work together.
The big question: Can they do that?
CNN Political Editor Paul Steinhauser: Can Romney broaden the electoral map?
This election will be won or lost in the battleground states. Or will it?
Mitt Romney's presidential campaign is making a last-minute push in two states that should be safe for Obama: Pennsylvania and Minnesota.
Romney campaigned in Pennsylvania on Sunday and goes back to the Keystone State on Election Day. Republican running mate Rep. Paul Ryan campaigned in Pennsylvania Saturday and in Minnesota on Sunday, and the campaign's up with ads in both states.
Is this a head fake by the Romney campaign, or do they see the tightening public opinion polls in both states as evidence they might be able to turn Pennsylvania and Minnesota from blue to red?
The Romney campaign says it's playing offense. The Obama campaign says the move is a sign of desperation by the Romney campaign. We'll find out who's right on election night.