Mitt Romney Donald Trump Presidential primaries and caucuses of the Republican Party took place within all 50 U.S. states, the District of Columbia, and five U.S. territories between February 1 and June 7, 2016.

The race was disrupted by the entry of Trump in June 2015, who quickly and unexpectedly rose to lead polls for the rest of the primary season, with the exception of a period in the fall when neurosurgeon Ben Carson experienced a surge in support.

[9] The pair won the general election on November 8, defeating the Democratic Party ticket of former secretary of state Hillary Clinton and her running mate, U.S.

In six states and territories, the first-instance popular vote did not allocate any delegates; they were elected later at local conventions and either bound to a candidate or uncommitted.

Donald Trump       Ted Cruz       John Kasich       Marco Rubio       Ben Carson     Tie       Uncommitted       No results (Colorado and North Dakota did not hold primaries/caucuses.)

Former Massachusetts governor Mitt Romney, the 2012 GOP presidential nominee, lost the 2012 election to incumbent Democratic president Barack Obama.

[89][90][91][92] Widely viewed as a very open contest with no clear front-runner, potential candidates fluctuated in the polls for an extended period from late 2012 to the end of 2015.

In the year prior to the election season, a total of 17 major candidates campaigned for the nomination, making it the single largest presidential primary field in American history at the time.

[87][97][98] Ohio governor John Kasich, a moderate Republican, remained in the race for an extended period despite being viewed as having little to no chance of winning the nomination.

[100][101] As April came to a close and Trump won a resounding victory in his home state of New York, both Cruz and Kasich were mathematically eliminated from winning the nomination without a brokered convention.

Both men then formed an alliance to block Trump from winning the nomination, ahead of the "Acela primaries" of five Northeastern states on April 26.

The possible candidates that fit this criterion included Bush, Gilmore, Kasich, Pataki, Walker and Christie, who in particular had been rising in popularity due to his loud and blunt manner of speaking at public events, championed by some as challenging conventional political rhetoric.

[115][116] In April 2014, Robert Costa and Philip Rucker of The Washington Post reported that the period of networking and relationship-building that they dubbed the "credentials caucus" had begun, with prospective candidates "quietly studying up on issues and cultivating ties to pundits and luminaries from previous administrations".

[117] Though Bush often polled in the low double digits, he was considered a prominent candidate due to his high fundraising ability, record as governor of Florida, a crucial swing state, and apparent electability.

[115][116] Shortly after Trump announced his candidacy on June 16, 2015,[124] many pundits noted his uniquely outspoken nature, blunt language and rhetoric, often directly contradicting traditional political candidates.

[125] After a few weeks of briefly matching Bush, Trump surged into first place in all major national polls by mid-July,[126] which he continued to lead consistently until November.

[135][136] Ten days later, on September 21, 2015, Walker suspended his campaign mainly due to his own poll numbers dropping after two lackluster debate performances.

By the third debate in late October, Bush and Fiorina's numbers were beginning to fade, while Cruz was on the rise and began coming in fourth by most poll averages.

[138] The third debate only solidified these numbers: Bush and Fiorina remained in low digits as both were considered lackluster, while Cruz was widely held as the winner and rose even further.

[148] The November 2015 Paris attacks, which killed 130 people days before Jindal dropped out, were widely seen as having a significant impact on the 2016 presidential race, particularly on the Republican side.

[138][152] By December, Cruz had overtaken Carson by solidifying a base of support among Christian conservatives and averaged national polling of 18%, second only to Trump.

Prior to the primary, Rubio picked up the key endorsement of Governor Nikki Haley, a feat seen as renewing his momentum after a disappointing finish in New Hampshire.

[178] Three days following the South Carolina primary, Trump won the Nevada caucuses, winning with 46% of the vote with Rubio in a distant second with 24% and Cruz slightly further behind with 21%.

[180] North Dakota held the last caucus on Super Tuesday, but there was no presidential straw poll and all the delegates elected later at its convention in April were unbound.

Carson did not win or place in any contest, netted only three delegates and though he initially expressed an intent to stay in the race, began showing signs of withdrawing in the days following Super Tuesday; he ultimately suspended his campaign on March 4, 2016.

[184] Meanwhile, as the prospect of a Trump nomination became more imminent, establishment Republicans pressured Romney or House Speaker Paul Ryan to enter the race.

[citation needed] The final debate between the candidates, which had been scheduled to take place on March 21, 2016, in Salt Lake City, was cancelled after Trump and Kasich withdrew from the event.

[207] On March 29, the same day Walker endorsed Cruz, at a GOP town hall event hosted by CNN, all three remaining Republican candidates distanced themselves from the vow they had taken in September to support their party's eventual nominee.

On April 5, buoyed by support from Walker and the state's talk and national radio hosts, Cruz won the statewide contests by a 48–35% margin and six congressional districts at the Wisconsin primary for 36 delegates.

[216] On April 28, 2016, a Trump rally in Costa Mesa, California, attracted protests that turned violent, with approximately twenty people arrested and a police car vandalized.