The battle for the United Kingdom's Conservative Party leadership has been transformed after former London Mayor Boris Johnson, who helped guide the U.K. out of the European Union, unexpectedly announced that he will not run for prime minister. "My role will be to give every possible support to the next Conservative administration to make sure that we properly fulfil the mandate of the people that was delivered at the referendum," Johnson said in a speech today, "and to champion the agenda that I believe in, to stick up for the forgotten people of this country." Johnson was at the forefront of the campaign in favor of “Brexit” and was widely expected to run for the party leadership. British politicians Theresa May, Michael Gove, Stephen Crabb, Liam Fox and Andrea Leadsom have so far confirmed that they are running for party leadership to succeed to Prime Minister David Cameron, who said he will step down later this year after his failed efforts to keep the U.K.