You mean as in "oath of fealty"?
Here is the result of "sufficiently loyal".
The truth is, there is about 30% of the voting public in each camp who vote for the party no matter what. The Republicans have so-called conservatives who would vote for Arlen Specter rather than Thomas Jefferson, because Specter is a Republican and Jefferson was a Democrat. On the Democrat side, they have a group who would vote for Zell Miller rather than Lincoln Chafee, because Miller is a Democrat and Chafee is a Republican.
Neither of these groups have any political clout. They are irrelevant to the political debate.
Neither party, nor any politician, has to work to get their vote. Consequently, their issues are of no concern to either party.
You've been had, and don't even know it!