2.5 million folks die every year. High percentage of them are old white people who vote Republican. Being replaced by non-whites that vote Dem 70% plus.
Or young voters (I don’t necessarily mean 18 year olds, but maybe late-20 early 30 year olds that haven’t been involved in the past) that are more on the libertarian side of the Republican spectrum. They find the disagreement over gay marriage and comments from Todd Akin offensive, but still believe in fiscal conservatism.
My mother was a lifelong Republican till the day she died. She’s voted Democrat ever since.