Hillary Clinton is expected to announce her candidacy for US president, ending prolonged speculation that she once again seeks to become the first woman elected to the White House.
Seven years after her bitter nomination defeat to Barack Obama, the former secretary of state and one-time first lady would enter the race on Sunday as the Democratic Party's overwhelming favourite, as Clinton and her rivals gird for a bruising, 18-month campaign slog.
Her announcement is expected to be delivered via social media - perhaps in a tweet - and accompanied by a campaign kick-off video highlighting her economy-focused political philosophy, according to US news outlets citing sources close to Clinton operations.
It is likely to trigger a donor deluge from a vast network of supporters who have long waited for her to officially enter the race, a move that would allow them to contribute directly to her 2016 election effort.
Clinton's campaign-in-waiting has organised for months behind the scenes, bringing on key staffers and advisers, plotting outreach operations and strategising.
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On Saturday, the campaign team hunkered down in Clinton headquarters in Brooklyn, New York, where upcoming campaign manager Robby Mook reportedly delivered a memo to staff urging teamwork in the months ahead.
"We are a diverse and talented family... and have each other's backs," the memo states, according to Politico, perhaps in an effort to avoid the infighting among top aides that marred Clinton's 2008 run.
On Saturday, she earned high praise from Obama himself.
"She was a formidable candidate in 2008. She was a great supporter of mine in the general election. She was an outstanding secretary of state. She is my friend," Obama said at a regional summit in Panama.
"I think she would be an excellent president."
Her Sunday announcement is expected to be followed by low-key campaign swings through Iowa and New Hampshire, states that hold the first votes early next year to determine the parties' nominees.
