Polls show Joe Biden ahead of Trump as he officially secures Democratic nomination for 2020 election

Joe Biden formally clinched the Democratic presidential nomination on Friday, setting him up against President Donald Trump in a presidential election to be held against a turbulent backdrop of a pandemic, economic collapse and civil unrest.

Mr Biden pulled together the 1,991 delegates needed to become the nominee for the November election after seven states and the District of Columbia held presidential primaries on Tuesday.

Mr Biden's official nomination came as a CNN poll of polls showed 51% of registered voters nationwide back him against 41% who support President Trump.

The poll of polls includes the five most recent national telephone polls measuring the views of registered voters.

The former vice president has effectively been his party's leader since his last challenger in the Democratic primary, Bernie Sanders, ended his campaign in April.

Mr Biden reached the threshold for his party's party nomination three days after the primaries because several states, overwhelmed by huge increases in mail ballots, took days to tabulate results.

He now has 1,993 delegates, with contests still to come in eight states and three US territories.

The moment was met with little of the usual fanfare, and while Mr Biden has started to venture out more this week, the coronavirus pandemic has largely confined him to his Wilmington, Delaware, home for much of the past three months.

Read more: Poll tracker: Will Donald Trump or Joe Biden win 2020 presidency?

The latest CNN Poll of Polls represent a shift in Biden's favor since April, when it found support for him averaging 48%, with Mr Trump averaging 43% support.

Three of the polls were conducted after the killing of George Floyd, which has sparked protests in Minneapolis and around the US over police brutality and racism against black Americans.

The other two polls were conducted in May, as the country struggled with the coronavirus pandemic and debated whether statewide lockdowns should continue for the sake of the public health or be lifted to boost the economy.

Elsewhere an average of reliable polls by Real Clear Politics puts Mr Biden seven percentage points ahead of Mr Trump. Barack Obama was around 2 points ahead at the same stage of his two successful presidential bids.

In the battleground states - where the election will actually be won or lost - it is just as bad. Polling for The Telegraph last month revealed that Mr Trump is behind in all six of the states he won by the narrowest margins in 2016.

The country faces the worst rate of unemployment since the Great Depression along side the civil unrest which erupted across the country following the death of George Floyd, a black man who died when a white Minneapolis police officer pressed his knee into Floyd's neck for several minutes.

This is the 77-year-old Mr Biden's third bid for the presidency and his success in capturing the Democratic nomination was driven by strong support from black voters.

He finished an embarrassing fourth place in the overwhelmingly white Iowa caucuses that kicked off the nomination process in February. Mr Biden fared little better in the New Hampshire primary, where his standing was so low that he left the state before polls closed on election night to instead rally black voters in South Carolina.

His rebound began in the more diverse caucuses in Nevada but solidified in South Carolina, where Mr Biden stomped Mr Sanders, his nearest rival, by nearly 29 points. He followed that with a dominant showing three days later during the Super Tuesday contests, taking 9 of the 13 states.

Mr Biden's strong showing in states such as North Carolina, Virginia, Tennessee and Texas reinforced his status as the preferred Democratic candidate of African American voters - but the relationship has not been without its strained moments. After a tense exchange with an influential black radio host, Mr Biden took sharp criticism for suggesting that African American voters still deciding between him and Mr Trump "ain't black".

That comment, and protests that have spread nationwide, have increased pressure on Mr Biden to pick an African American running mate. He has already committed to picking a woman as a vice presidential candidate.

Black voters are unlikely to back Mr Trump over Mr Biden by a wide margin. A recent Fox News poll shows just 14 per cent of African Americans who are registered to vote have a favorable opinion of the president compared with 75 per cent who favorably view Mr Biden.

But Mr Biden must ensure that black voters are motivated to show up to the polls in November, especially in critical swing states that narrowly went for Mr Trump in 2016.

At one point, the Democratic primary included dozens of candidates of different races, genders and generations and an openly gay man. The contest was dominated by debate over unapologetically progressive ideas, including fully government-funded health care under "Medicare for All" and a sweeping proposal to combat climate change known as the "Green New Deal".

Mr Biden prevailed by mostly offering more moderate approaches that he argued would make him more electable against Mr Trump.

He refused to budge on his rejection of universal health care and some of the Green New Deal's most ambitious provisions to combat climate change.

Since clinching the nomination, however, Mr Biden has worked to build his appeal among progressives, forming joint task forces with Mr Sanders' campaign to find common ground on key issues like health care, the economy and the environment. Mr Biden has also embraced a plan to forgive millions of Americans' student debt, meaning that he clinches the nomination as easily the most liberal standard bearer the Democratic Party has ever had.

Mr Biden's embrace of his party's left flank could help him consolidate a Democratic base that remained deeply divided after the 2016 primary and ultimately hurt Hillary Clinton in her defeat to Mr Trump. But it could also undermine Mr Biden's attempts to rebuild the Obama coalition, which is often loosely defined as minorities and young people, as well as educated Americans and some working-class voters.

The former vice president has sought, since announcing his candidacy, to cast the election as a battle "for the soul of the nation," and promised to restore order and dignity to the White House while rehabilitating the US image on the world stage. Such an approach, though, necessarily focuses on being more of an alternative to Mr Trump than offering radically new political ideas. And that further underscores Mr Biden's difficult task of trying to unite his party's base while appealing to voters from far beyond it.