It's four weeks until election day in the United States, more than 3 million people have already voted and Joe Biden has extended his lead over Donald Trump in the national polls after seven remarkable days in the race for the White House.

It's only a week since the presidential candidates clashed on stage in Ohio, in a debate featuring insults, interruptions, personal attacks – and little substantive discussion.

Post-debate polls suggest Biden came out on top with voters, though most pundits agreed there were few real winners from a messy 98 minutes during which Trump failed to denounce white supremacy.

The Amtrak-loving Democrat then hit the rails with a day of campaigning through Ohio and Pennsylvania on a train, while the president held a rally in Minnesota and mingled at a big-money fundraiser at one his golf clubs in New Jersey.

Soon after it emerged that Trump adviser Hope Hicks had tested positive for COVID-19, and in a tweet early on Friday morning the president revealed he and first lady Melania had also been infected.

Multiple others with close contact to the White House, including Press Secretary Kayleigh McEnany, later announced they had tested positive of the virus, which is suspected to have been spread at an event marking the nomination of Amy Coney Barrett for the Supreme Court.

Amid confusion over the timeline of Trump's diagnosis and the details of his health, the president was flown to Walter Reed National Military Medical Center from where he tweeted videos and drove out of the facility for a photo op as he attempted to portray strength at a time of vulnerability.

Biden – who has repeatedly tested negative for COVID-19 over the past week and pulled down attack ads against the president following his diagnosis – is 7.8 points ahead nationally according to CGTN analysis, and eyes will now turn a vice-presidential debate between Republican Mike Pence and Democrat Kamala Harris on Wednesday that takes on increased importance. 

Trump returned to the White House on Monday, claiming "I feel better than I did 20 years ago!" – but both his health status and his capacity to campaign in the closing weeks are unclear. In-person events can be ruled out for the president in the near future and the chances of the second debate with Biden going ahead as scheduled on October 15 are in the balance.

The two biggest stories of the year – the election and the pandemic – are now more closely entwined than ever before. As Trump continues to receive treatment for COVID-19, the world is waiting to find out how his health develop and how American voters will react to an unprecedented situation just weeks from the polling day.

Video: Wang Zengzheng and Zhou Tingyu

Script: John Goodrich

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