Trump And Cruz Lead Republican Field

With just over 40 days before the Iowa caucuses, it is impossible to predict how the presidential race will shake out. But it is not hard to tell which way the wind is blowing.

A Quinnipiac University poll released on Tuesday was notable less for what it said about the candidates and their standings than what it revealed about the segments of the electorate they represent. Donald J. Trump and Senator Ted Cruz of Texas  led the poll — by a wide margin — with 28 percent and 24 percent, followed by Ben Carson, who received 10 percent.

That is a combined 62 percent of a Republican primary electorate in which just 8 percent of voters professed to be undecided. Many voters say they might change their minds, however. Mr. Trump’s supporters, by and large, were not among them. About 63 percent of his supporters said their minds were made up, compared with just 36 percent for Mr. Cruz.

Of the so-called establishment candidates, Senator Marco Rubio of Florida led with 10 percent. Gov. Chris Christie of New Jersey got 6 percent, and Jeb Bush got 4 percent — a combined 20 percent of support.

Those figures are worrisome to those who had hoped this was going to be a presidential cycle in which insurgent candidacies could be contained.

Though Mr. Cruz has gained in several recent Iowa polls, it is still unclear whether he, Mr. Trump or someone else will emerge as the victor the night of the Iowa caucuses. Public opinion polls tend to change greatly in the lead-up to votes, and polls in later states change very quickly after the first contests take place.