Fact: Glioblastoma claimed the lives of senators John McCain and Ted Kennedy.
Conclusion: Sometimes even cancer has a positive outcome.
If a brain disease kills enough brain cells it can turn a Republican into a Democrat, however no diseased Democrat brain has ever gone Republican. The more brain cells killed the more likely someone becomes a Democrat which points to a casual relationship. After 100% of the brain cells have died the odds of voting Democrat increases to 100%.