Survey report

When Pew Research Center first asked Republican voters their preferences for the GOP presidential nomination in March 2015, just 1% volunteered Donald Trump as their first choice.

Thirteen months later, Trump was the first choice of 44% of Republican and Republican-leaning registered voters, more than any of his rivals. Today, 88% of these voters back him in the general election against Hillary Clinton.

At an overall level, Trump’s rise may appear linear; his support increased in the aggregate with each survey over the course of the primary. But in actuality, individual voters’ preferences over this period were quite fluid.

This report and accompanying interactive is based on a longitudinal analysis of the primary and general election preferences of Republican and Republican-leaning registered voters in Pew Research Center’s nationally representative American Trends Panel. This approach provides a window into change and stability in voters’ choices at an individual level over the course of six surveys conducted throughout 2015 and 2016. For more detail, see Methodology used in this report.

From March 2015 to April 2016, nearly all Republican voters changed their minds at least once about who they were supporting for the GOP nomination.

This volatility was not confined to the early stages of the GOP nomination contest. A 61% majority of GOP voters changed their minds at least once across the three surveys conducted from December 2015 to April 2016, as key primary contests were unfolding. A quarter of Republicans changed their minds twice in this period.

Only 34% of Republican voters supported the same candidate at all three points, including 23% who consistently backed Trump over this period – which is by far the largest share “sticking” with a candidate.

The result is a portrait of the fluidity in voters’ decision-making throughout the primary process. Some voters changed their allegiance by necessity, when their preferred candidate dropped out of the race. But others shifted their preferences, from survey to survey, among the active candidates.

In the case of Trump, his overall share of support grew throughout the primary process as he gained support from voters who had backed other candidates or had previously been undecided. But he also lost ground. Trump held on to 70% of his supporters between August and December of 2015, while 30% of those who had supported Trump in August went on to support other candidates or to say were undecided in December. This “churn” in candidate preference was not limited to Trump; all candidates gained, and lost, support during this period.

This volatility continued into the primary season. Aside from the 23% of voters who backed Trump consistently across three surveys between December and April, and the 7% of GOP voters who consistently backed Ted Cruz, no single pattern stands out. The accompanying graphic illustrates some of the hundreds of paths that voter preferences took over this period.

Patterns of primary support and the general election

By the April survey (conducted April 5-May 2), when only Trump, Cruz and John Kasich remained in the race for the Republican nomination, Trump was supported by 44% of GOP voters: 23% had consistently supported him since December, while 21% had not.

Of the remaining 56% of Republican voters, 44% had not named Trump as their first choice in any of the three surveys (December, March or April), including 39% who had named another candidate in at least one survey (just 5% of Republican voters were consistently undecided during this period). An additional 12% of GOP voters had named Trump their preferred nominee in either December or March, but then did not support him in April.

Overwhelming majorities of Republican voters in each of these groups now prefer Trump to Clinton in a general election matchup. However, the intensity of that support varies. Nearly all of those who were loyal supporters of Trump since December (98%) say they will vote for him against Clinton – and 91% are certain they will do so. By contrast, a smaller share of voters who did not support Trump in any of these three surveys back him in the general election: 79% do so, and only 53% of those in this group say they are “certain” they will vote for Trump over Clinton.

Steady Trump supporters, latecomers and skeptics

Throughout the primaries, surveys regularly showed that Trump garnered more support from GOP voters who had not attended college, those who were less religiously observant and men.

The patterns of support over the course of the primaries show that those in these groups were more likely than others to back Trump early on and stay with him.

While 30% of Republican voters who have not attended college backed Trump across all three surveys between December and April, just 15% of Republican college graduates were early – and consistent– backers of the presumptive GOP nominee.

Republicans who frequently attend religious services were less likely to be steady supporters of Trump in this period. Just 15% of Republican voters who attend services weekly backed Trump consistently, compared with 28% of GOP voters who attended services less often.

Conversely, college educated and more religiously observant Republicans are more likely to have not backed Trump in any of these three surveys. Fully 57% of those who attend services regularly fall into this skeptical group, compared with just 36% of those who attend less regularly. Among Republicans with a college degree, about half (53%) also did not back Trump in any of these three surveys, compared with 39% of those without a college degree.

The American Trends Panel (ATP), created by the Pew Research Center, is a nationally representative panel of randomly selected U.S. adults living in households. Respondents who self-identify as internet users and who provided an email address participate in the panel via monthly self-administered Web surveys, and those who do not use the internet or decline to provide an email address participate via the mail. The panel is being managed by Abt SRBI.

Members of the American Trends Panel were recruited from two large, national landline and cellphone random-digit-dial (RDD) surveys conducted in English and Spanish. At the end of each survey, respondents were invited to join the panel. The first group of panelists was recruited from the 2014 Political Polarization and Typology Survey, conducted January 23rd to March 16th, 2014. Of the 10,013 adults interviewed, 9,809 were invited to take part in the panel and a total of 5,338 agreed to participate.¹ The second group of panelists was recruited from the 2015 Survey on Government, conducted August 27th to October 4th, 2015. Of the 6,004 adults interviewed, all were invited to join the panel, and 2,976 agreed to participate.²

Participating panelists provided either a mailing address or an email address to which a welcome packet, a monetary incentive and future survey invitations could be sent. Panelists also receive a small monetary incentive after participating in each wave of the survey.

The analyses in this report depend upon six separate surveys (fielded in March, August and December 2015 and March, April and June 2016). The data for 5,544 panelists who completed any of these six waves were weighted to be nationally representative of U.S. adults. In this report, results for December 2015 and later are based on all 2,079 Republican and Republican-leaning registered voters who responded to any of these six waves. Results for March and August 2015 are based on the 1,345 Republican and Republican-leaning registered voters who were members of the ATP at the time.

The ATP data were weighted in a multi-step process that begins with a base weight incorporating the respondents’ original survey selection probability and the fact that in 2014 some panelists were subsampled for invitation to the panel. Next, an adjustment was made for the fact that the propensity to join the panel and remain an active panelist varied across different groups in the sample. The third step in the weighting uses an iterative technique that matches gender, age, education, race, Hispanic origin and region to parameters from the U.S. Census Bureau’s 2014 American Community Survey. Population density is weighted to match the 2010 U.S. Decennial Census. Telephone service is weighted to estimates of telephone coverage for 2016 that were projected from the January-June 2015 National Health Interview Survey. Volunteerism is weighted to match the 2013 Current Population Survey Volunteer Supplement. It also adjusts for party affiliation using an average of the three most recent Pew Research Center general public telephone surveys. Internet access is adjusted using a measure from the 2015 Survey on Government. Frequency of internet use is weighted to an estimate of daily internet use projected to 2016 from the 2013 Current Population Survey Computer and Internet Use Supplement. As a final step, the data for the 3,472 the March/August panelists were poststratified so that the distribution of voter preferences for December 2016 matches the distribution for full set of 5,544 respondents.

Panelists who did not respond to all of the surveys used in this report are missing data for their vote preference for waves in which they did not participate. These missing values were imputed using the process described below.

Sampling errors and statistical tests of significance take into account the effects of both weighting and imputation. Interviews are conducted in both English and Spanish, but the Hispanic sample in the American Trends Panel is predominantly native born and English speaking.

The following table shows the error attributable to sampling, weighting and imputation that would be expected at the 95% level of confidence for different groups in the analysis. The margins of error shown reflect the largest margin of error for any of the shifts in support to or from each candidate at each point in time:

In addition to sampling error, one should bear in mind that question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of opinion polls.

Pew Research Center is a nonprofit, tax-exempt 501(c)(3) organization and a subsidiary of The Pew Charitable Trusts, its primary funder.

About the missing data imputation

The American Trends Panel is composed of individuals who were recruited from two large, representative telephone surveys originally fielded in early 2014 and late 2015. Participants in the panel are sent surveys to complete about monthly. While wave-level response rates are relatively high, not every individual in the panel participates in every survey. The analyses in this report are based on six surveys (fielded in March, August, and December 2015 and March, April, and June 2016).

Of the more than 5,500 respondents who participated in at least one of the waves in which we collected primary vote preference, several hundred respondents (between 12 and 15 percent) did not participate in any given wave. A statistical procedure called hot deck imputation was used to guard against the analysis being undermined by this wave level nonresponse. In particular, there is some evidence that those who are most likely to participate consistently in the panel are more interested and knowledgeable about politics than those who only periodically respond. Omitting the individuals who did not participate in every wave of the survey might overstate the amount of stability in individuals’ preferences.

The particular missing data imputation algorithm we used is known as “hot deck” imputation. This algorithm identifies individuals who are very similar to those with missing data and sampling from the similar observed cases to fill in responses for the missing cases. For each case where the vote preference is missing, the algorithm searches for other cases that are similar along several dimensions (demographic: sex, age, race/ethnicity; socioeconomic: education; political attitudinal: partisan identity, ideological consistency, interest in politics, political knowledge; and geographic: census region, urban/suburban/rural; primary preference in other waves). After identifying a small set of similar individuals the algorithm selects one at random to serve as a “donor,” and fills in the missing preference with the value from the donor case. The imputation procedure was restricted to individuals who belonged to the panel during the same time period (e.g. March and August 2015 primary vote preferences were not retroactively imputed for panelists who joined in late 2015).