Florida Sen. Marco Rubio is the latest to declare his candidacy for president. The 43-year-old Republican made his announcement on Monday at Miami's Freedom Tower, one day after Democrat Hillary Rodham Clinton declared she's throwing her hat into the presidential race for the second time. 

MIAMI, FL - APRIL 13: U.S. Sen. Marco Rubio (R-FL) announces his candidacy for the Republican presidential nomination at the Freedom Tower on April 13, 2015 in Miami, Florida. (Photo by Joe Raedle/Getty Images)

Rubio's candidacy brings to three the number of Republicans who have formally entered the race, while as many as five others are still pondering it.

Among them, Gov. Chris Christie who will be in New Hampshire this week trying to convince activists and voters that he can win the Republican presidential nomination in a crowded primary where he appears to have been outmaneuvered by likely rivals before the race has technically begun.

Christie plans to hold a town hall meeting in New Hampshire on Wednesday.

The Associated Press contributed to this report.