The US presidential campaign steps up a notch on Wednesday with the first televised debate. A month before Americans go to the polls on 6 November, here are five key things to know.
1. There's one big issue
As many as 80% of voters rate the economy as very important to how they vote, according to research published last week by polling company Rasmussen Reports.
"The biggest issue is the economy, and jobs is one part - a very important part - of that," says Scott Rasmussen. "It's not just concern for people that don't have a job - 28% of workers are worried they might lose their job soon.
"And there's the housing market. Only 47% of homeowners believe their home is worth more than the mortgage, which is an unbelievable figure in America. We were taught we would grow up, buy a home and watch the equity grow, so many people feel betrayed."
One-term presidents Jimmy Carter and George Bush Sr left the White House when the economy struggled, the latter with Bill Clinton's de facto slogan "the economy, stupid" ringing in his ears.
Unemployment has remained stubbornly above 8% for 43 months and federal debt has passed $16tn, leading many commentators to wonder why Obama is not behind in the polls. Or to question whether the economy is really as big an issue as voters say it is.
The figures are not all doom and gloom, says Rasmussen. "Americans don't feel they are better off than they were four years ago, but they don't feel they are worse off either, and that's why the election is so competitive."
But just because the president is not behind in the polls doesn't mean the economy is not a big issue, he adds. Many people who think Obama has done a poor job are just not sure Romney would do any better.
Plus, a number of Americans still blame George W Bush for the economic problems.
2. Only a few states matter
It's all about the so-called swing states, or battleground states, because much of the US is heavily Democrat or Republican, and therefore unlikely to change hands.
Ohio, which has unemployment below the national average, has gained mythical status as the bellwether state, having correctly picked the successful presidential candidate in every election since 1960. With 18 electoral college votes, spending by both parties in this state has been in the tens of millions of dollars.
Ohio households have been receiving automated telephone calls from campaigners twice a week for six months. And every evening, prime time television is dominated by campaign adverts.
"I've lived in half a dozen different states but never seen this saturation between TV, radio and other media," says Tim Gaddie, 37, a doctorate student at Ohio's Bowling Green State University who works at a local history museum,
"For the last election, I was in Indiana and it's definitely more involved here. The most annoying thing is the phone calls, but there's something to be said for it all. I'm glad that people care enough to be involved and have a discussion."
There are two Americas during the election campaign - the one where it's hard to escape the bombardment of campaign slogans and messages, and the one where life goes on almost as normal.
3. The electorate is changing
Every month there are 50,000 more Hispanics eligible to vote in the US. The Hispanic community passed the 50m mark in 2010, which is 16.3% of the national population.
This is the first election when both candidates have appeared on Spanish language television, in a forum on immigration.
In 2008, Obama received 68% of the Latino vote and he's expected to get roughly the same backing this time around, says Gabriel Sanchez, an expert in Latino politics at the University of New Mexico.
"The question isn't whether Romney can capture enough of the Latino vote to win, but whether the Latino turnout will be high enough for the president to win."
Mindful that Romney's tougher stance on immigration could be costing Latino votes, influential Republicans like Jeb Bush have called for a softening in tone when dealing with this issue, saying "demographics are destiny" and can't be ignored.
Senator Lindsay Graham has put it more bluntly: "We're not generating enough angry white guys to stay in business for the long term."
4. It's not just about the US
Foreign policy is still regarded as a second-tier issue among US voters, although the killing last month of the US ambassador to Libya, Christopher Stevens, has pushed it up the campaign agenda, with Iran, Israel and Afghanistan now being widely discussed on US networks.
Romney, who was accused of being opportunistic in attacking Obama after the death of Stevens, says the president has been soft on Iran and has betrayed Israel.
He has also vowed to get tough with China over what he calls "currency manipulation", raising the prospect of a trade war.
"In an electorate as large and as diverse as the US, there will always be some hot-button foreign policy issue," says Shaun Bowler, professor of political science at the University of California Riverside.
"For example, you might see Arab-Americans who will be very motivated by discussions of Palestine, or Cuban-Americans very motivated by policy towards Cuba.
"In the current period there is still scope for foreign policy to play a role - Iran's nuclear programme and Israel's reaction, maybe Syria will spin out of control or maybe there will be terrorist outrages. These will bring foreign policy to the fore."
There is huge international interest in who occupies the White House because the actions of a US president have a global impact.
5. Whoever wins, expect more gridlock
The presidential election is not the only ballot on 6 November. All the seats in the House of Representatives and a third of the Senate seats are being contested.
While these races haven't received as much attention, they could be crucial to the success of an Obama or Romney presidency.
Republicans control the House and Democrats the Senate, so unless either changes hands, the recent impasse could continue - so few bills were passed in 2011, it was called the "do-nothing Congress".
This inertia, most prominently illustrated by the failure a year ago to reach a long-term agreement on the debt ceiling, has contributed to historically low Congress approval ratings among Americans.
"The whole checks and balances design makes for a very protracted policy-making process, even when there is unified party government, and that is by design," says Bowler. "That's a background feature of US politics that makes it very different from most European countries."
The level of blockage recently has been high, even by US standards.
But the former president, Bill Clinton, struck an optimistic note when he told CNN last week that he expected a more co-operative atmosphere in Congress after the election.