Pollsters have a variety of tools at their disposal to understand how voters feel about political leaders. The gold standard for elected officials is usually job approval, where people give an up or down vote on how they think someone has done in office. People can be asked what attributes they think leaders have, ask if they trust them to handle various issues, or very broadly can be asked if they are favorable or unfavorable, a metric known in the business as the “fav-unfav.”

But there’s another metric used by researchers that can help understand at an emotional level how people respond to a person or group: a feelings thermometer. In situations where someone might feel that saying they feel “unfavorable” to someone is too strong (for instance, asking people about views on sensitive topics like race or religion), a feelings thermometer lets people express wariness toward a subject without making them come out as plainly negative.

Pew Research Center, over the course of the last few years, has been asking voters if they feel “warm” or “cool” toward Donald Trump, then tracking whether the temperature has gone up or down since. And the results underscore just how firmly President Trump has held onto his base.

In the wake of the Helsinki summit last month, I tackled the question of whether or not Trump’s supporters would abandon him and suggested that the only way the incident would harm him with his supporters is if they came to view his actions as “weak.” And while there were a few high-profile defections, most polls showed Republican voters lining up in support of their president, generally approving of his actions. The president’s numbers did not move much in the wake of the summit.

My skepticism that Helsinki would truly damage the president with his party, or drive many more people away from the GOP, was due in part to what I have been seeing and hearing in research into Republican voters since Trump's inauguration. Yes, many don’t like the tweeting. Yes, many wish he wouldn’t insult quite so many people all the time. But overall, I have heard more than a few voices pop up in focus groups of those who readily admit Trump was not their first — or even 16th — choice in the Republican primary, who nonetheless have come around to feeling warmly toward him.

Pew’s new work puts data behind these anecdotes. In their survey, they have panelists who they verified did in fact vote in the 2016 election and, contemporaneously, said they voted for Trump. Pew was able to take this group and look at how they had responded over time. In April of 2016, in the heat of the GOP primary fight, Trump was viewed “very warmly” by only about 43 percent of those who would go on to vote for him. Fully one-third of his eventual voters felt neutral to cool toward him at that point.

But since that time, Trump’s voters have not grown weary of him, dismayed by a presidency they aren’t sure they signed up for. To the contrary, comparing those April 2016 figures to the ratings given to him by his voters in March 2018 shows that he has won a fair share of “converts”, those who moved from a neutral or cool position during the primary and who now feel warmly toward their commander in chief. While there are still skeptics — the 12 percent of his voters who didn’t like him then, don’t like him now, and who Republicans ought to be quite worried about in the midterm elections — the number of Trump voters who have cooled on him is small, only 6 percent in Pew’s analysis.

Those who didn’t vote for Trump in November 2016 feel ice cold toward the president. Half say they feel “very” cold toward him. And yet, this is the dilemma then that has been faced by Republicans throughout the primary season: There is simply nothing to be gained inside the party from criticizing Trump. Most Trump voters who were no fans of his in the primary season, who may have been Sen. Marco Rubio, R-Fla., or Sen. Ted Cruz, R-Texas, supporters and figured they just needed to fall in line, have not cooled on him since.

Republican candidates are feeling the heat as we finish out summer and move into the home stretch of the midterm elections. They’ll need to win over voters who feel more lukewarm on the president in order to hold on in November. And yet, the Republican base they need to turn out feels warmer than ever toward the president.