Kamala Harris - and Democrats - face an unprecedented task with 100 days to election

When Joe Biden addressed the NAACP convention in Las Vegas last week, one of his biggest applause lines - a line that set off chants of "Four more years!" - was when he praised Kamala Harris as "not only a great vice-president" but someone who "could be president of the United States".

Now she has that chance.

On Sunday, when the president made the extraordinary decision to end his re-election campaign, he made an equally momentous choice: to offer his "full support and endorsement" of Harris to be the Democratic nominee and take on Donald Trump in November.

"It's time to come together and beat Trump," the 81-year-old president said. "Let's do this."

The announcement, just weeks before the Democrats are set to formally choose their nominee at the convention in Chicago, has plunged an already tumultuous contest deeper into unchartered waters - while thrusting his would-be successor into the spotlight.

"I am honored to have the president's endorsement and my intention is to earn and win this nomination," Harris said. "I will do everything in my power to unite the Democratic party - and unite our nation - to defeat Donald Trump and his extreme Project 2025 agenda."

With just over 100 days until the November election, the task before her is monumental and unprecedented. An assassination attempt on Trump has united Republicans behind him, and appears to have strengthened his hand as Democrats dissolved into a rancorous debate over Biden's fitness to serve.