President Joe Biden withdrawing from his campaign for re-election opens up the Democratic nomination at a crucial time in the election calendar. There are four weeks until the Democratic National Convention where the party will confirm their candidate for the presidency. It's important for the Democrats to show unity now and not descend into a period of damaging in-fighting, so it seems highly likely they will select Vice President Kamala Harris who Biden and other senior Democrats have already endorsed.

Although not all Democrats have shown enthusiasm for Harris up until now, there will likely be a surge of support as she becomes the candidate. There will be relief that Biden has stepped aside so a younger, more dynamic candidate can compete in the election. The politics of race, gender, and ethnicity are already central to the election and as the first black woman to run for president who also has South Asian heritage, Harris will be uniquely positioned to speak to those agendas and appeal to important sectors of the electorate. The Democrats will also attempt to use her background as a prosecutor and her experience in the Senate and as Vice President to show her strength as a candidate ready to be president. Who she picks as a running mate will also be crucial to the Democrats chances of defeating Donald Trump on November 5 - balancing the ticket with a candidate from one of the Midwest swing states could make a particularly significant difference.

Trump and his running mate JD Vance have already indicated that they will continue to campaign on the record of the Biden administration, emphasising the role of Harris as VP if she does become the Democratic candidate. They argue that Biden-Harris have led the worst presidential administration in US history. They're also continuing to criticise Biden for staying on in the White House - he plans to complete the remaining 6 months of his presidency. Biden stepping aside in the race suddenly makes things much harder for Trump though, not least because the age and competency concerns that were focused on Biden might now be turned onto Trump. The 78 year old has promoted himself as robust and strong, especially after surviving the recent assassination attempt, but he will now go to the polls as the oldest American to ever run for president. That is unlikely to affect the deep support he has among core Republican voters, but it may be a factor the Democrats can now exploit to help fire up their own supporters and convince undecided voters not to cast their ballots for Trump in November.