Hillary Clinton will take another stab at cracking what she calls "the highest and hardest glass ceiling" on Sunday when she starts a long-awaited second run for the White House as the prohibitive Democratic front runner.
Clinton's campaign for the November 2016 election will emphasize her plans to address economic inequality and will tout the historic nature of her bid to become the first woman US president, aides say.
But after decades in the public eye as the wife of former President Bill Clinton, a US senator and secretary of state, she could face a challenge in showing a more down-to-earth side while connecting with ordinary voters.
Clinton will also have to quell a controversy over her work use of a private email account while secretary of state, which Republicans have said is a sign of her penchant for secrecy.
Clinton has said she used the single email account for convenience and should have used government email, but violated no rules.
Hours before the much-anticipated announcement on Sunday, potential Republican opponents took swings at Clinton over her years guiding US foreign policy as secretary of state under President Barack Obama.
"We must to do better than the Obama-Clinton foreign policy that has damaged relationships with our allies and emboldened our enemies," said former Florida Governor Jeb Bush in a video released by the political action committee Right to Rise.
Bush, brother to former President George W Bush, is currently exploring a presidential bid.
Kentucky Senator Rand Paul, who formally began his campaign for the Republican nomination last week, made the rounds of Sunday talk shows to slam Clinton's handling of a 2012 attack on a US diplomatic compound in Benghazi, Libya.
Clinton, who lost a heavyweight Democratic nominating battle to Barack Obama in 2008, will announce her campaign on video and social media, a Democrat familiar with her plans said. She will travel later in the week to Iowa, which holds the first nominating contest in early 2016.
In a memo made public on Saturday, Clinton's campaign manager Robby Mook told staff while the goal was for Clinton to win the presidency, the campaign was not about her but "everyday Americans".
"We are humble: we take nothing for granted, we are never afraid to lose, we always out-compete and fight for every vote we can win. We know this campaign will be won on the ground, in states," he said in the campaign memo, titled "We Are Hillary for America".
Many Democrats have eagerly awaited Sunday's announcement since the day in June 2008 when Clinton pulled out of her primary battle against Obama with an expression of regret that she could not crack "that highest and hardest glass ceiling this time".
On Saturday at the Americas summit in Panama City, Obama said at a news conference that Clinton would make an "excellent president."
Opinion polls show Clinton has a huge lead over potential 2016 Democratic rivals, and few are expected to enter the race.
A Reuters-Ipos tracking poll shows Clinton backed by more than 60 percent of Democrats. US Senator Elizabeth Warren of Massachusetts, a favorite of liberals but who says she is not running, is a distant second at 18 percent.
So far, former Maryland Governor Martin O'Malley and former U.S. Senator Jim Webb of Virginia, whose support languishes in single digits in polls, are the most prominent contenders to take steps toward challenging her.
Republicans have been gearing up for the battle, and a big field of Republican presidential contenders is expected.
Senators Ted Cruz of Texas and Rand Paul of Kentucky have been the first to formally enter the race, and Senator Marco Rubio of Florida will jump in on Monday.
Clinton operatives have already begun reaching out to top bundlers to urge them to start calling people in their donor networks, a source familiar with the matter said. At least one West Coast bundler began making calls to top donors this past week, and will place another round of calls after the announcement Sunday, the source said.