Not only are the differences between Republican/Democrat not that great, but in the last 50 years they have largely swapped constituencies!

It started when JFK pushed civil rights. This made Democrats popular with Northern civil rights activists. Nixon took advantage of this with his "Southern strategy" that used the issue as a wedge to get Southerners to vote Republican for the first time ever. (Previously the South wouldn't vote Republican because they held the Republicans responsible for the Civil War.) The swap cascaded from there as each successful candidate got there by appealing to what had once been the other party's base. (Reagan took a particularly chunk, hence the phrase "Reagan democrat".)

The swap completed with George Bush.