The most important vote is the very first one that determines who is in the majority—who controls the committees, the floor votes, everything. So even a Republican who votes with you 0% of the time is better than a Democrat who votes with you 0% of the time, because they help you with your majority status. Way better. And in practice a GOP Senator from a blue state will vote with you at least some more often than will a Democrat from that same blue state.
Trust me, no Democrat who gets elected in Maine would ever have done what Susan Collins did with Kavanaugh. Even red state Democrats didn’t, knowing they were going to lose because of voting against him.
It is stupid to run a conservative Republican in a deep blue state who has no chance of getting elected.
But it is even more stupid to elect a Republican in a deep red state who won’t be a 100% reliable conservative vote.
Candidates should be as conservative as possible while being electable.
Assuming the Republican votes with a Republican majority. Our side seems to always have the crossers, never the Dems.