Are Pro-Life Democrats Categorically Unreasonable?

Robert George asserts that "however much one might dislike Republican policies in other areas, it’s clear that the death toll [from embryo destructive research] under the Democrats would be so large as to make it unreasonable for Catholic citizens, or citizens of any faith who oppose the taking of innocent human life, to use their votes and influence to help bring the Democratic party into power."  I respect this view (and greatly respect the scholar offering it), but it raises a few questions for me:

First, is it "unreasonable" for pro-life citizens to vote for Democrats because Republicans' policies in other areas such as immigration, welfare, taxes, the environment, and foreign policy are at least arguably morally acceptable, or does the degree of harm threatened by Democrats in this single area render Republicans' policies in other areas irrelevant?  For example, if President Bush expressly endorsed the torture of suspected terrorists but maintained his opposition to embryo destructive research, would reasonable pro-life citizens still be "bound to Republicans?"   

Second, is it prudent (or even possible) to quantify and rank the harms threatened by the federal funding of embryo destructive research versus the harms threatened by other immoral government policies as a bright-line equation for determining a single acceptable voting option?  For example, if President Bush authorized a preemptive invasion of a nation in a manner that conflicted with just war principles, should the resulting civilian casualties be tallied as harms facilitated by a citizen's support of his administration given the certainty of the casualties, even though they were not specifically intended?  If tax cuts and opposition to minimum wage increases could be conclusively demonstrated to diminish the ability of certain citizens to maintain a standard of living consistent with human dignity, could the negative impact on human flourishing be entered into the equation even though it falls short of a literal destruction of human life? 

Third, does the effect of single-issue voting actually deter the party on the wrong side of the issue, or by effectively shutting down the competition for votes on other issues, does it give license to the party on the correct side of the issue to disregard other pressing moral concerns without fear of reprisal on election day?

Rob