President Barack Obama is within reach of the 270 electoral votes needed to win a second term, as polls also show that he is in the lead. His rival, Republican Mitt Romney, must overturn an increasingly narrowing margin. To overtake Obama, Romney would need to gain the upper hand in nearly all of the nine states in which he and Obama are competing the hardest.

Polls show the president with a steady lead in many of them as Romney looks to shift the dynamics of the race, starting with their first debate in Denver.

Obama drew more than 11,000 people to an evening rally in Nevada, a Western battleground state. But Romney’s running mate, Paul Ryan, says there’s time for the Republican ticket to win. “In these kinds of races people focus near the end, and that’s what’s happening now,” he said in a recent news interview.

A prominent Romney supporter, New Jersey Governor Chris Christie said he expected Romney’s debate performance in Denver to shake up the campaign after a “tough couple of weeks”. Christie predicted Romney would do “extraordinarily well,” and that come tomorrow morning, “this whole race is going to be turned upside down”.

But a top Obama adviser, David Plouffe, cast doubt on how much the debate would turn around the race, saying that even if Romney did put in a monumental performance in the debates, it would not be enough. An Associated Press analysis shows that Obama would win at least 271 electoral votes, with likely victories in crucial Ohio and Iowa along with 19 other states and the district of Columbia. Romney would win 23 states for a total of 206.

To oust the incumbent president, Romney would need to take up-for-grabs Florida, Colorado, Nevada, North Carolina, New Hampshire and Virginia, which would put him at 267 votes, and then beat Obama in either Ohio or Iowa.

In the US, presidents are elected not by national popular vote but in state-by-state contests. Each state gets one electoral vote for each of its representatives in the House and Senate. There are 538 votes in the Electoral College, and a candidate must have at least 270 to win. Except for Maine and Nebraska, states award all their electoral votes to the candidate who wins the state.

In the final weeks before the 6 November vote, Obama is enjoying a burst of momentum and has benefited from growing optimism about the economy as well as a series of Romney stumbles. Most notably, a secret video surfaced recently showing the Republican nominee telling a group of wealthy donors that 47% of Americans pay no federal income taxes and consider themselves victims dependent on the government.

Early voting is under way in dozens of states, and national and key state surveys show undecided voters feel more favourably toward Obama than Romney. The race is not yet over, but it is looking good for President Obama.