If they are incapable of affecting influence or change on the issue, then I guess they should stop using it as a campaign issue.
They are capable of affecting change, and they do. It's just that the change they promise on and deliver on is not up to everyone's expectations.
Example:
Repubs had been campaigning on a promise to ban partial birth abortions since at least 1992 (I think - my memory may be a bit foggy). They passed bans through congress 2 or 3 times under Clinton, only to have the bills vetoed. In 2003, the Repubs made good on their promise by passing the ban through congress and having it signed into law by GWB. This ban was one of the biggest pro-life changes to abortion law in a good long while, and it goes about as far as the supreme court has allowed the congress to go on this issue. (Details
here)
So, substantive change was promised, and after much hard work those promises were delivered on. Yet some still feel the Repubs have made no meaningful effort to deliver on their abortion promises and aren't deserving of continued support over the issue. I can only presume that these folks have unreasonable expectations, and that if the hard fought victories to date do not satisfy then nothing ever will.