I have a hunch.. that whenever a US election comes around more people will vote for (R) no matter what than (D), it's like the Democrats have to win a large majority of undecided voters every time.. correct me if im wrong?
you're sort of on the right track there.
There are not as many republicans, but they are much more organized and ideologically similar, so they function more like a bloc.
There are more democrats, but they represent more of a coalition of different groups, i.e. minorities, women, the LBGT community, the Jewish community, etc. etc. Because they are so diverse, they don't always agree on everything and naturally is not as united or as organized as the republican party.