In the W Bush era it was gays getting married. Terrorists are taking over and gays are gonna shack up and destroy America. Gotta have a foreign and domestic set of enemies to get people riled up about.

But the Overton Window shifted and no one really cares if the gays marry.

Trans people are even fewer than gay people and there may be a number of real, or kinda real, arguments to be had there, such as the wisdom of giving younger kids hormones, or if trans athletes should be allowed to participate in gendered sports leagues. They make a fantastic wedge issue, with the benefit that they're 0.3% of the population -- political footballs, with no chance of actually burning a voting block.