Two that come to mind are nicotine and marijuana research. To be clear both sides of the political spectrum try to rig or block scientific research for political goals, so neither one has a monopoly on that, which is why I am opposed to ANY govt funding of science. Its not a proper function of govt.
The LEOs blocked research into marijuana use for pain, nauseousness, etc. for decades because they don't want to admit that they dedicated their lives to a pointless "war" on drugs and they still heavily influence what gets studied today.
The anti-tobacco scare-mongering is beyond belief. Researchers admit that nicotine is not the "most addictive drug in the world" per the propaganda, they can't even get rats addicted to it in isolation. It turns out it is nicotine plus chemicals in tobacco smoke that make smoking addictive and the cognitive and physiological benefits of nicotine are just starting to be known. The big problem here is that if research legitimizes nicotine use (even as a pill or whatever) it can threaten the cigarette taxes that many states depend on so it is opposed which is a pretty cynical way to fund your govt in my book. The "second hand smoke" hysteria is statistical non-sense pushed by the anti-tobacco zealots.
I think the climate research is politically tainted as well but I won't go into that.