WASHINGTON: Hillary Rodham Clinton promptly set off on the campaign trail after making her long awaited entry into the 2016 presidential race, and her potential Republican rivals wasted no time offering blistering criticism of the former secretary of state.

Clinton, seeking to become America’s first female president, announced her candidacy Sunday and left on a roughly 1,000-mile (1,600-km) trip from her New York home to Iowa, the Midwestern state that kicks off the long, state-by-state contest for the Democratic nomination.

In a video message announcing her candidacy, Clinton promised to serve as the “champion” of everyday Americans in a country with growing income inequality.

Clinton appears unlikely to face a formidable Democratic opponent in the primary elections. Should she win the nomination, Clinton would face the winner of a crowded Republican primary field that could feature as many as two dozen candidates.

Kentucky Sen. Rand Paul, a favorite among libertarians, and Texas Sen. Ted Cruz, a champion of the right-wing tea party movement, have already entered the Republican race.

Senator Marco Rubio told donors Monday that he is launching a US presidential campaign, becoming the latest — and youngest — Republican in the race to succeed Barack Obama in the White House.

US media reported that Rubio told donors on a conference call, hours ahead of a glitzy launch event in Miami, that he is a next-generation candidate, separating himself from other older contenders like fellow Floridian Jeb Bush and Democrat Hillary Clinton.

Republicans were already trying to counter the former first lady’s strong resume by casting her as someone who is not trustworthy. They have jumped on her use of a personal rather than a government e-mail account and a server located in her home while she was President Barack Obama’s first secretary of state. They have also raised questions about donations from foreign governments to the Clinton family’s foundation.

Some Republicans sought to make foreign policy an issue at a time when the Obama administration is negotiating a nuclear deal with Iran and moving to restore diplomatic relations with Cuba.

“We must do better than the Obama-Clinton foreign policy that has damaged relationships with our allies and emboldened our enemies,” said former Florida Gov. Jeb Bush in his own online video Sunday. Bush, the brother and son of former presidents is widely expected to join the race for the Republican nomination.

While there are serious policy differences among the dozen or so major Republicans considering a run for president, they appear to have all concluded there’s little downside in starting early when it comes to going after Clinton — an opponent that only one of them has the chance to potentially face.