I've noticed a trend thats been occuring since the 90s. What's up with all the Democrats that transplant/move to a Republican state, often change the demographics of a state? Examples are Californians moving to Oregon, Washington and Nevada. Before the '88 election, they were fairly moderate states.
Before the '92 election, to say nothing of '88, California was a largely GOP state.
This has less to do with Dem transplants, and more to do with the changing face of the two parties. When the Dems moderated on economic issues, and the Republicans embraced social conservatives, a lot of northern states with sizable moderate Republican populations trended D. While Dem transplants have made a difference in places like Nevada (which is largely a matter of Latino immigration, and thus not entirely comparable) and along the south Atlantic coast in places like Virginia and South Florida, you really can't use them to explain places like Oregon and Washington.
One place where Republican in-migration might make a difference down the road is in the Twin Cities exurbs.
I'd argue that demographic and other broader social trends had a lot to do with the parties changing.