Rubio's bid is the fourth in a series of similar announcements over the past weeks, following those of fellow Republicans — Texas Sen. Ted Cruz and Kentucky Sen. Rand Paul, — and former Democratic Secretary of State Hillary Clinton.
The four are largely considered to be front-runners in the White House race, alongside with ex-Florida Gov. Jeb Bush, Wisconsin Gov. Scott Walker, and New Jersey Gov. Chris Christie – all Republicans. Their official entrances are expected to come in following months.
Marco Rubio, 43, was to announce his bid at an event in Miami, Florida. Rubio is known for his conservative stance on financial and social issues, and support of initiatives to balance the federal budget. He opposes curbs on US defense spending and criticizes same-sex marriage.
With incumbent US President Barack Obama facing the end of his two-year constitutionally-mandated term limit and a US Congress in control of the Republicans, many presidential hopefuls from the GOP field have been emboldened to run for their party's nomination in the 2016 race.
The 2016 White House race was kick-started in March by Texas Sen. Ted Cruz announcing his candidacy for the Republican nomination. Cruz, a Canada-born Tea Party favorite of US-Cuban descent, hopes for the support of a "new generation of courageous conservatives," as he explained in a 30-second video clip.
The 44-year-old has been a reliable opponent of President Obama. In September 2014, he delivered a 21-hour marathon speech against the president's groundbreaking healthcare reform policy. Last month, he introduced legislation that would make it easy to reimpose and tighten US sanctions against Iran, in an attempt to overturn a nascent landmark nuclear deal, slowly being accomplished during Obama's tenure.
Cruz's bid for nomination was followed by fellow Republican and Kentucky Sen. Rand Paul, and Democratic ex-Secretary of State Hillary Clinton earlier this month. The three are largely considered to be front-runners in the presidential race, alongside with ex-Florida Gov. Jeb Bush, Wisconsin Gov. Scott Walker, Florida Sen. Marco Rubio, and New Jersey Gov. Chris Christie – all Republicans. Their official entrances are expected to come in following months.
Rand Paul, a 52-year-old ophthalmologist and Kentucky lawmaker, is a son of Ron Paul, who ran unsuccessfully for the US presidency in 2012. He advocates tax and military budget cuts, though he recently changed his tune and suggested drastically increasing military spending by 16 percent ahead of seeking the Republican nomination.
Hillary Clinton, a 67-year-old presumptive Democratic favorite, set off her presidential campaign in a Sunday announcement on social media that came hours late and contained awkward typos. However embarrassing, this has been the first Democratic bid so far.
The former First Lady lost the 2008 presidential race to Obama and then served as a top US diplomat under his presidency from 2009 to 2013. Her time in this capacity was partly overshadowed by the 2012 attack on a US diplomatic mission in the Libyan capital that led to the killing of the US ambassador.
Clinton took responsibility for security lapses, but controversially wiped some of attack-related emails. She came under new criticism in March 2014 after she was found to have used a private email hosted at her home server to send out official letters, in what could be a violation of the federal open records law.
But despite Clinton's comparisons between her secretive style and that of former Republican president Richard Nixon, she maintains a solid lead against any potential Democratic primary opponents with over 60 percent in favor of her nomination, according to polls.
If elected she would be the first woman to be chief executive of the United States.
Florida Sen. Marco Rubio, 43, is among Republican lawmakers considering a presidential run. He is due to announce his entrance at an event in Miami, Florida, later on Monday. Rubio is known for his conservative stance on financial and social issues, and support of initiatives to balance the federal budget. He opposes curbs on US defense spending and criticizes same-sex marriage.
Last week, Bush made headlines after US newspapers published his 2009 voter registration form where the former Florida governor identified himself as Hispanic. This has been considered an overreach by the presumable presidential hopeful, who is a fluent Spanish speaker, as he tried to secure Latino votes.
New Jersey Gov. Chris Christie, 52, is a moderate Republican believed to nurture presidential hopes. A recent NBC/Wall Street Journal poll showed that just over 30 percent of Republicans would support his nomination. In late March, Christie said he was still considering a possible run, while media expect him to face off Jeb Bush over the GOP center ground.
Wisconsin Gov. Scott Walker, 47, is considered to be a dark horse in the 2016 presidential race. He has been making moves to join in the campaign, going out to key primary states of Iowa and New Hampshire, where he reportedly edged out his possible Republican challenger Jeb Bush in a recent NH1 poll. Walker stated earlier this year he will scrap any deal with Iran that did not bar it from building an atomic bomb. He also called security on the US-Mexican border a top priority.
More incoming bids for a Republican nomination may still come from former Arkansas Gov. and ordained Baptist minister Mike Huckabee; South Carolina Sen. Lindsey Graham, a foreign policy hawk and interventionist; African-American neurosurgeon and evolution skeptic Ben Carson; Hewlett-Packard's former CEO and the Republican Party's only female bidder Carly Fiorina; as well as Obama's 2012 rival, former Texas Gov. Rick Perry.
Jim Webb, a 69-year-old former Virginia senator and incumbent US Navy Secretary, launched his campaign website, saying he has been urged to run for president by people from across the US political spectrum. On his campaign trip to Iowa, the Vietnam vet pledged to help the working class.
Massachusetts Sen. Elizabeth Warren, 65, could become the second female presidential candidate from the Democrat pool and the third woman in the White House race, although she herself has repeatedly denied any intention to run for president.
Former Maryland Gov. and Baltimore Mayor Martin O'Malley, 52, is rumored to be planning to challenge Clinton in 2016, though he has not officially announced a campaign. In 2012, he signed a law legalizing same-sex marriages in Maryland.
Bernie Sanders, a 73-year-old independent senator from Vermont, caucuses with the Democratic Party. In an interview with The Nation last year, he said he was "prepared" to run for president, but has never launched a campaign.
