They are a white Christian party while white Christians are making up less of the population as a whole.
It doesn’t mean the party as a whole is racist, by any means, it means the agenda is largely one of white Christians. 75 – 80 % of Jewish voters vote Democratic. Latino voters go Democratic at a 2 to 1 proportion and Asian voters go Democratic at a 60 % rate. Add in college educated whites that Obama won and you begin to have a problem over time. That doesn’t mean none of this will change as coalitions are fluid, but if it doesn’t change Republicans will face similar problems nationally that they face in Illinois.