December 23 – Jimmy McMillan, perennial candidate from New York changes party affiliation from Democratic to Republican and officially announces his candidacy for the presidential nomination of the Republican Party[5][6][7]
January 12 – Herman Cain, radio host, businessman and former Senate candidate from Georgia, announces the formation of a formal exploratory committee in preparation for a possible run for the presidential nomination of the Republican Party.[9]
January 18 – Randall Terry, an anti-abortion activist from New York and former Republican, officially announces his candidacy for the presidential nomination of the Democratic Party[10][11]
March 3 – Newt Gingrich, former Speaker of the House of Representatives, announces the formation of an informal exploratory committee in preparation for a potential run for the presidential nomination of the Republican Party.[15]
Buddy Roemer, former Governor of Louisiana, announces the formation of an exploratory committee in preparation for a potential run the presidential nomination of the Republican Party[16][17]
March 16 – Secretary of State Hillary Clinton expands on her previous statement to also specify that she will not serve as vice-president or a second term as Secretary of State[18]
March 21 – Tim Pawlenty, former governor of Minnesota, announces the formation of an exploratory committee in preparation for a potential run for the presidential nomination of the Republican Party;[19][20] Fred Karger announces he will run for president.
March 23 – Fred Karger officially announces his candidacy for the presidential nomination of the Republican Party.[21]
April 11 – Mitt Romney, former governor of Massachusetts, announces the formation of a formal exploratory committee in preparation of a potential run for the presidential nomination of the Republican Party;[25] The St. Anselm College Republican Straw Poll in Goffstown, New Hampshire is won by Fred Karger with 25% of the vote, followed closely by Romney with 23%[26]
April 13 – Rick Santorum, former senator from Pennsylvania, announces the formation of a formal exploratory committee in preparation of a potential run for the presidential nomination of the Republican Party[27]
April 18 – Roy Moore, Chief Justice of the Alabama Supreme Court, announces the formation of a formal exploratory committee in preparation for a potential run for the presidential nomination of the Republican Party[28][29]
April 26 – Ron Paul announced the formation of a formal exploratory committee in preparation for a run for the presidential nomination of the Republican Party[31][32]
June 14 – Michele Bachmann, U.S. Representative of Minnesota, announces during the debate that she has filed papers with the Federal Election Commission for a run for the presidential nomination of the Republican Party[49]
June 18 – Results of the Southern Republican Leadership Conference straw poll: Ron Paul 612; Jon Huntsman 382; Michele Bachmann 191; Herman Cain 104; Mitt Romney 74; Newt Gingrich 69; Sarah Palin 41; Rick Santorum 30; Tim Pawlenty 18; Gary Johnson 10; Buddy Roemer 9; Thad McCotter 2[50]
June 21 – Jon Huntsman officially announces his candidacy for the presidential nomination of the Republican Party[51][52]
July 1 – Thaddeus McCotter, U.S. Representative of Michigan, announces he has filed papers with the Federal Election Commission to campaign for the presidential nomination of the Republican Party[56][57]
July 2 – Thaddeus McCotter officially announces his candidacy for the presidential nomination of the Republican Party.[58][59]
July 21 – Buddy Roemer officially announces his candidacy for the presidential nomination of the Republican Party[60][61]
August 12 – Republican candidates debate is held in Iowa. Bachmann, Cain, Gingrich, Huntsman, Paul, Pawlenty, Romney, and Santorum are the participants[62]
September 7 – Republican candidates debate is held in Simi Valley, California. Bachmann, Cain, Gingrich, Huntsman, Perry, Paul, Romney, and Santorum are the participants[68]
September 12 – Republican candidates debate is held in Tampa, Florida. Bachmann, Cain, Gingrich, Huntsman, Perry, Paul, Romney, and Santorum are the participants[69]
September 14 -Arizona Governor Jan Brewer issues an official proclamation that the Arizona primary shall be held on February 28
September 19 -Ralph Nader and others announce a coalition to find a primary challenger for Obama.[70]
September 22 – U.S. Representative Thaddeus McCotter announces his withdrawal from the race for the Republican presidential nomination[71][72]
September 22 – Republican candidates debate is held in Orlando, Florida. Sponsors: Fox News, Google and Florida Republican Party. Participants: Bachmann, Cain, Gingrich, Huntsman, Johnson, Perry, Paul, Romney, and Santorum[73]
September 26 – Herman Cain wins Florida 5 straw poll.[74]
October 4—Chris Christie, Governor of New Jersey, responding to mounting speculation that he would make a late entry in the Republican presidential nomination race, announces he will not run for president in 2012[75][76]
October 11— Republican candidates debate on Bloomberg Television at Dartmouth College in Hanover, New Hampshire. Sponsored by Bloomberg, The Washington Post and WBIN-TV.
October 12— Michele Bachmann, Herman Cain, Newt Gingrich, Gary Johnson, and Rick Santorum, all address the New Hampshire House of Representatives[80]
— Democratic candidates debate in Goffstown, New Hampshire, Sponsored by Saint Anselm College[86] President Obama does not participate
December 19— Gingrich narrowly wins Tea Party Patriots straw poll over Michele Bachmann[87]
December 28— Former New Mexico Governor Gary Johnson ends his bid for the Republican presidential nomination, and enters the race of the Libertarian Party's presidential nomination[88]
January 3 – The Iowa Republican caucuses are initially declared as a victory for Mitt Romney. However, later counts show Rick Santorum with a small lead in the popular vote. Later, Ron Paul picks up a majority of delegates at the state's convention. The Iowa Democratic caucuses are won by Barack Obama. Neither caucus awards any delegates, but are to be used as a guide for delegate selection in June's party conventions
January 4 – Representative Michele Bachmann announces the suspension of her presidential campaign
January 16 – Jon Huntsman withdraws from the race and endorses Mitt Romney
January 16 – Recount in Iowa shows that Rick Santorum won the Republican caucuses
January 16 – Republican debates at the Myrtle Beach Convention Center in Myrtle Beach, South Carolina, sponsored by Fox News and the Republican Party of South Carolina
January 19 – Rick Perry withdraws from the race and endorses Newt Gingrich
January 19 – Republican debate in Charleston, South Carolina, sponsored by CNN and the Southern Republican Leadership Conference
February 7 – The Missouri Democratic Primary and Minnesota caucuses are won by Barack Obama. The Missouri Republican Primary is won by Rick Santorum, although the contest does not affect how Missouri's GOP delegates are awarded
April 3 – Maryland, Wisconsin, Washington DC primaries – won by Mitt Romney and Barack Obama, the latter of whom won enough delegates to clinch the Democratic nomination.
April 10 – Former US Senator Rick Santorum suspends his campaign for the Republican presidential nomination[94][95]
May 2 – Former Speaker of the House of Representatives Newt Gingrich suspended his candidacy for the Republican presidential nomination and endorsed Mitt Romney[101]
December 17 – The electors meet in their respective state capitals (electors for the District of Columbia meet within the district) to formally vote for the president and vice president.
January 4 – Electoral votes formally counted before a joint session of Congress; the President of the Senate formally announces the electoral result. (Constitution mandates this to occur on Jan. 6; since that is a Sunday in 2013 Congress voted to change it to Jan. 4 [113])