When you vote for a candidate, you are responsible for whatever policies they enact ... to the extent that you could have foreknown or predicted them based on the positions the person has publicly articulated and/or various attitudes he has demonstrated in the past.
This is only true if you take an extremist view of what democracy is - that your "elected representative" literally represents you in everything. I don't view democracy as a matter of electing "representatives".
No, this is true due to the nature of the moral act of voting.
Let's take this to its logical conclusion then.
Imagine 2 candidates:
A - believes in abortion, ritual human sacrifice, public sodomy, polygamy, total suppression of all Christian religion, slavery . . .
B - opposes all of these resolutely, except abortion.
Now let's say that hypothetically, unless you vote for B, A will win the election. Do you refuse to vote B because you can't have a pro-abort as your representative? I think it would be highly immoral for you to refuse to vote B in such circuмstances.