Political commentators have asserted for months that Donald Trump’s dominance of the Republican presidential field is fueled by his anti-immigrant rhetoric. As Thomas Edsall put it:

Donald Trump’s success is no surprise. The public and the press have focused on his defiant rejection of mannerly rhetoric, his putting into words of what others think privately. But the more important truth is that a half-century of Republican policies on race and immigration have made the party the home of an often angry and resentful white constituency — a constituency that is now politically mobilized in the face of demographic upheaval.

This is a very plausible hypothesis, but one with little comprehensive evidence to date. Now, thanks to a collection of survey data from YouGov, we can show how, and how much, voters’ concern about immigration has helped Trump.

The YouGov data includes 14 surveys that were conducted every week or every other week between June 13 and Nov. 9. In these surveys, the most frequent question about immigration asks respondents to rate the issue’s importance.