Joe Biden is leading in the states he needs to win but the Democrats have been here before

Joe Biden, who will officially accept the Democratic nomination for U.S. president on Thursday, enjoys a wide lead in the polls over Donald Trump, the Republican incumbent. Biden has the edge an often significant one in all the states he needs to secure the White House. If these numbers hold through to Nov. 3, a Democrat will be in the Oval Office come January.

That all might sound a little familiar.

Trump has been the underdog in the polls before. He trailed Hillary Clinton for most of the presidential election campaign in 2016 before he defied the odds and pulled off a stunning upset.

But just because it happened before doesn't mean it will play out the same way this time. Every election is different particularly one held in the midst of a pandemic.

According to the CBC's newly launched Presidential Poll Tracker, an aggregation of all mainstream national U.S. polls,Biden has the support of 52.5 per cent of decided voters. With Trump standing at 43.6 per cent support, Biden has a lead of 8.9 percentage points.

At this point in the last election cycle, Clinton's lead over Trump stood at just 6.1 points in the 2016 iteration of the Poll Tracker and never got as wide as Biden's current lead. Clinton also never surpassed the 50 per cent mark among decided voters.

Trump's time in office before the COVID-19 pandemic struck had already taken a toll on his popularity. At the beginning of the year, only about 42 to 43 per cent of Americans approved of the president's performance, according to FiveThirtyEight's polling averages, making him the least popular president at the tail end of his first term since Harry Truman.

Approval of his handling of the pandemic as well as the anti-racism demonstrations across the country have not improved those numbers. On the pandemic itself, about 58 per cent of Americans disapprove of Trump's handling of it. That's about four points worse than his overall disapproval rating.

Swing states leaning to Biden

Trump's management of a series of crises in the U.S. has helped push Biden ahead by considerable margins in more than enough states he needs to win the White House.

U.S. elections are not decided by which candidate gets the most votes but rather by the candidate who receives the most electoral college votes. Each state is awarded a number of electoral college votes equal to their number of members of Congress (plus three votes for Washington, D.C.) and the candidate that receives the most votes in each individual state is awarded all of that state's electoral college votes. There are 538 votes up for grabs, meaning 270 is enough to win.

The Presidential Poll Tracker puts Biden's electoral college vote total at 308 in states in which he leads by at least five points, putting him well over the 270-vote mark. Those states do not include Arizona, Georgia and North Carolina where he has a lead of less than five points. They add another potential 42 electoral college votes to his total.

• Presidential Poll Tracker: Get all the latest numbers here

The map is looking good for Biden at the moment. States deemed "likely Democrat" by the Poll Tracker, which indicates a lead of between five and nine points, include Florida, Michigan, Pennsylvania and Wisconsin, states won by Trump in 2016, sealingClinton's fate.

That the list of toss-ups states with a margin of less than 2.4 points between the leading candidates includes big states like Texas and Ohio, as well as Iowa, show how the map has widened since 2016. Trump's margin of victory in that election was eight points in Ohio and nine points in both Iowa and Texas.

That doesn't mean Biden can take victory for granted. He is doing better than Clinton was at this stage in a number of states, particularly those in the South and southwest like Georgia, Texas and Arizona.

But he's doing worse than Clinton in the U.S.Midwest. His margin with Trump is two points lower than Clinton's was at this point in 2016 in Iowa and Pennsylvania, three points narrower in Michigan and Minnesota and four points tighter in Wisconsin and Ohio.

Trump still likely has an electoral college advantage if the race tightens

That the race is tighter in the Midwest than in 2016 could be due to a number of factors including a change in how pollsters are weighting the surveys. The 2016 polling miss was primarily due to this region of the country. It could be that Trump has shifted what a Republican voter looks like, appealing to a white working class that was more Democratic in the past.

But it does highlight how the electoral college could still play a decisive role in the outcome of this election.

Biden does have some wiggle room. The Poll Tracker estimates Biden's lead could tighten to as little as three points and he would still be favoured to win the electoral college.

Any tighter than that, however, and Trump could pull off the same upset as he did in 2016. With a margin of less than three points, Trump would be narrowly favoured to win the electoral college which he did in 2016 despite losing the popular vote by two percentage points.

But to get to a race of less than three points, Trump can't count on a polling miss alone. He will have to move the numbers between now and election day, as a miss with the same benefit to him as in 2016 would not be enough to overturn Biden's advantage.

And polls aren't always off in the same direction. If Biden beat his polls by as much as Barack Obama did in 2012, the Democrats could win in a landslide.

After 2016's surprise, second-guessing the polls will undoubtedly be a feature of the U.S. campaign between now and November. The lessons of the last election are always the freshest, even if every campaign is different.

But there are plenty of other significant sources of uncertainty over how the next 11 weeks will unfold, including how COVID-19 could influence public opinion and Americans' ability to vote in the first place.

Right now, Trump is the underdog, just as he was four years ago. But, unlike in 2016's election, nobody will be under-estimating him or, with COVID-19 still looming, confidently predicting how it will all play out.