Hillary Clinton is running for president in the 2016 election, a top aide said Sunday.
John Podesta, a top adviser to the former secretary of state, made her plan official with an email Sunday to donors and supporters of her first presidential campaign in 2008.
Clinton later formally announced her campaign for the Democratic Party's presidential nomination with an online video posted on social media. Sources said she is planning to travel to key early voting states, including Iowa and New Hampshire.
If elected, Clinton would become the first woman to serve in the Oval Office.
It will be Clinton's second presidential bid after her failed effort in 2008, when Barack Obama won the party's nomination on his way to becoming president.
Speaking from Panama Saturday, President Obama said Clinton would make an "excellent president."
"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. I think she would be an excellent president," he said.
A recent Gallup poll found 48 percent of those surveyed have a favorable impression of Clinton, her lowest rating since 2008. Forty-two percent of those polled had an unfavorable rating of her.
Ahead of the announcement, Republicans tried to link Clinton to Obama, a regular focus of GOP criticism.
"We must 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, a potential Republican candidate, in a video Sunday.
Kentucky Senator Rand Paul, who launched his presidential campaign last week, pointed to the Clinton family's foundation, saying it was hypocritical for the Clintons to accept from Saudi Arabia, which places public restrictions on female movement and activity.
"I would expect Hillary Clinton if she believes in women's rights, she should be calling for a boycott of Saudi Arabia," Paul said on NBC's Meet the Press. "Instead, she's accepting tens of millions of dollars."
The former Secretary of State could turn out to be a lot more hawkish on U.S. foreign policy - issues like Iran, Israel, Syria and Libya - than Obama, analysts said.
“I think that Secretary Clinton will actually try to convey a sense that she is tougher, stronger, more experienced, more professional,” said political analyst Stuart Rothenberg of the Rothenberg and Gonzales Political Report.
But the road to victory for the former first lady could be rocky.
Clinton is perceived by some as unapproachable. Her decision to launch her campaign on YouTube is not going to help that image, said Lara Brown of the Graduate School of Political Management at George Washington University.
“I don’t know that I would project this image of 'I’m prepackaged behind a video' to start this campaign,” Brown told VOA. “I would think she would want to have real people there, that she would want to be in a boisterous but enthusiastic environment.”
Clinton's presidential campaign will center on boosting economic security for the middle class and expanding opportunities for working families, while casting the former senator and secretary of state as a "tenacious fighter" able to get results, two senior advisers said Saturday.
The senior advisers, who spoke on condition of anonymity in order to discuss her plans ahead of Sunday's announcement, provided the first preview of the message Clinton planned to convey when she launches her long-anticipated campaign on Sunday with an online video.
The strategy described by Clinton's advisers has echoes of Obama's 2012 re-election campaign. He framed the choice for voters as between Democrats focused on the middle class and Republicans wanting to protect the wealthy and return to policies that led to the 2008 economic collapse.
The advisers said Clinton will argue that voters have a similar choice in 2016. Clinton also intends to sell herself as being able to work with Congress, businesses and world leaders.
That approach could be perceived as a critique of Obama. He has largely been unable to fulfill his pledge to end Washington's intense partisanship and found much of his presidency stymied by gridlock with Congress.
Speaking on U.S. news shows Sunday, Secretary of State John Kerry praised his predecessor for the "terrific job" she did in repairing global ties while she was America's top diplomat.
Clinton "did a terrific job of rebuilding alliances that had been shredded over the course of the prior years," Kerry told ABC's This Week.
But Kerry stressed that as the nation's top diplomat he was out of politics, and it was not for him to endorse any candidates.
Calling Clinton "a good friend," Kerry told NBC's Meet the Press that "she's highly qualified, and I'm confident we'll wage no matter what, with or without a primary, a formidable campaign."
Clinton's unlikely path to political office began on the sidelines, as the wife to then Governor of Arkansas Bill Clinton who would go onto serve two terms in the White House.
Both Yale Law School graduates, the Clintons were a departure from more traditional political couples. During his 1992 campaign, Clinton promised voters that they would get “two for one,” by voting him into office but quickly dropped that claim when it proved unpopular.
Reporters covering the White House noted Clinton's involvement, her unofficial role as primary adviser to the president - an observation bared out in thousands of photos of the Clintons deep in conversation.
Her biggest initiative while her husband was president, national health care reform, fell apart without coming to a vote in Congress.
Emerging from the shadow of her husband in 2000, first lady Clinton went on to become candidate Clinton, carving out a career as a politician representing New York in the U.S. Senate for eight years. It was the first for a former first lady, and the start of many firsts in her career.
By the summer of 2008, Clinton, now a failed presidential candidate was ready to consider former rival Obama's offer to appoint her Secretary of State.
The international stage would prove far more welcoming to Clinton, who appeared to find her stride, crisscrossing the globe for talks with world leaders and demonstrating a command of foreign affairs. In her new capacity as the U.S.'s top diplomat, Clinton saw her approval ratings soar, reaching 66 percent in 2010.
The burst of approval a few short years after the public's rejection of her presidential ambitions, the triumphs followed by potentially career ending lows, have been a constant in her more than two decades in public life.
By 2012, Clinton was again on the defensive, answering to Republicans in congress about the Obama administration's handling of attack on the U.S. diplomatic compound in Benghazi, Libya.
So far, no other strong Democratic candidates have emerged in the 2016 campaign, but there are some two dozen Republicans fighting for the chance to defeat her at the polls.
On the Republican side, Senators Ted Cruz and Rand Paul have announced their intention to run for their party's nomination, and Senator Marco Rubio is widely expected to join them on Monday. Others expected to join what analysts say will be a crowded Republican field include former Florida governor Jeb Bush and Wisconsin Governor Scott Walker.
Some material for this report came from AP and Reuters.