Racial purity concerns of some Catholics aside.
The Protestant vote has only gone democrat 3 times, while the Catholic vote has only gone republican about 5 times.
Race isn't the factor, and the denomination is not based on race, and we are importing millions of Catholics.
Race IS the factor. All things being equal. If Demographics had not changed dramatically since 1980, Romney would have won in a landslide in 2012 just simply by carrying the white vote by 20%. As whites continue shrink in the electoracte, so do GOP fortunes. The Democrats have won the popular vote in the last 5 out of six elections, no doubt largely to changing demographics, and an electorate more interested in getting free stuff and less concerned about higher taxes and deficit spending.