The maths is pretty simple. 35% of the public and 74% of republican-and republican-leaning, that would make the republican leaning about (given that some of the democrat leaning people wanted the wall too) at about 40-45% of the respondents. I do not know how the polling is conducted, but allow for some true independents, and it mirrors the result of the latest election fairly well, a good deal of more democrat votes. Now, considering the fact that they may also have obtained answers from people who did not actually vote, because of reasons, and the non-voting population tends to lean a bit more democrat (No numbers here, just based on reports during the election period, might be wrong), the numbers are not at all far off. (Of course, classic under-representation of people not answering because they are ashamed of voting for the guy with the hair might also factor in.)