A fierce US presidential campaign in battleground states has come to a close after presidential candidates, President Barack Obama and Republican Mitt Romney, on Monday wound up their campaign rallies.

The 2012 election campaign will go down in history as the first to record billions of dollars in campaign funding by the respective candidates. By October 17, 2012, the two candidates had declared over $2 billion in campaign funding, with over $700 million more spent by Political Action Committees (PACs).

PACs raise and spend campaign funds outside the mainstream political campaign groups as a result of their having been prohibited from direct ties with political parties. PACs were created after a decision in 2010 by the Supreme Court favoured the right to donate unlimited funds for political campaigns by individuals and groups.

Whilst the presidential candidates are expected to declare the origin of their funds, the powerful PACs are not obliged to disclose their donors, a case for which they have been widely criticised.

Super PACs wield immense power over campaign policies, as threats from them (especially in the area of advertising) could undermine a party's potential. Most PACs have spent resources on attacking political adversaries, and as a result this campaign -according to analysts- has been one of the most vitriolic.

Advertising campaign costs by pro-Republican external campaign groups and super PACs went beyond $300,000 in favour of Mitt Romney ahead of the elections. The total amount spent on campaigns will be known after the election.

To ensure a trouble and fraud-free election, the Chicago Election Board will have more than 300 investigators assigned to election day duty

As Electoral officials prepare for the presidential election on Tuesday across the nation, Chicago, home city of President Obama, will be expecting a total number of 1.3 million people registered to vote in this election.

The Chicago City Board of Election Commission said on Monday that voters will start casting their vote early on Tuesday morning and will run until 7PM. The ballots will be counted after the close with the results expected 45 minutes later.

While the majority of Chicago voters are expected to vote for Obama, Republican candidate Romney has toiled to leave no stone unturned in Florida, a key state in deciding the ultimate winner.

On Monday Obama traveled to Wisconsin, Madison as part of his last leg of campaigns as Romney continued his tour of Florida. Barack Obama also has his eyes set on Florida.

The battlegrounds for the two presidential candidates are the swing states of Ohio and Virginia, which have proved a very tough struggle. Election analysts argue that if either of the candidates fails to clinch a win in these states they are unlikely to become the president of the US.

Meanwhile, like in other states, the Chicago City Board of Election Commission has called on voters who witness any irregularities or encounter a problem on election day to call the boards.

"The election boards have nearly a full complement of Republican and democratic judges of election for each precinct, plus a contingency of more than 200 standby judges who will be able to help fill in any unexpected vacancies," said the board.

"To ensure a trouble and fraud-free election, the Chicago Election Board will have more than 300 investigators assigned to election day duty,"

Their investigators, the board said, will be making unannounced inspections of polling places and responding to calls from voters and election judges for assistance,"

The US presidential election is decided by the Electoral College and each state is given a number of electoral votes in proportion to its population. And to win, a presidential candidate is expected to get 270 electoral votes.

On Tuesday, Americans will also elect a handful of governors, House of Representatives and one-third of the Senate, where Republicans are expected to keep control of the House of Representatives, while Democrats will control the Senate.

University professor, Kenneth Mayer, said around 120 million Americans are expected to cast their vote in the 2012 presidential election.