RAND Paul, the libertarian Republican senator from Kentucky, announced on Tuesday that he will run for president. He is the second major Republican candidate within two weeks to officially declare his intention to enter the 2016 race following the earlier announcement by Texas Senator Ted Cruz, the Tea Party favourite.

Although general election day remains over a year and a half away, Mr Paul's announcement is the clearest sign yet that the Republican field is beginning to mobilise to replace Barack Obama in what appears likely to - ultimately - be a political fight for the White House against Democrat Hillary Clinton. Mr Paul and Mr Cruz could prove strong candidates, but will potentially face a very large field of others for the Republican nomination in what is shaping up to be one of the most competitive of the party's races for president for a generation.

The other contenders for the Republican crown who are formally exploring the possibility of a run include former Florida governor Jeb Bush, the brother and son of former presidents George W and George HW Bush respectively; the Governors of Texas, New Jersey, and Wisconsin, Rick Perry, Chris Christie and Scott Walker respectively; and businessman Donald Trump. Others who have expressed interest in joining the fray include US Senator Marco Rubio from Florida, former US Ambassador to the United Nations John Bolton, business executive Carly Fiorina, and US Representative Peter King of New York.