A populist politician, whose objective is to redistribute income, seeks the highest tax rate possible on rich investors without losing 51 percent of the vote (or a few points more, perhaps, depending on the value of the margin of safety). A smaller tax increase that wins more of the vote unnecessarily leaves money on the negotiating table. Similarly, a politician aiming to lower taxes on rich investors seeks the largest tax cut that still capture 51 percent of the vote.
Nixon was the last Republican president before voters contested Roe. Without the 15 percent bloc of evangelical Christian voters in his back pocket, Nixon had to assent to a 70 percent marginal tax rate to capture 51 percent of the vote. Even then, he only won the election because of the unpopularity of the Viet Nam War. Eisenhower only won by accepting a 90% marginal tax rate. Clinton was the first Democratic president in office after voters contested Roe. With only 85 percent of the vote available to him, where 40 percent of that vote supported tax reduction, Clinton could only support marginal tax rates as high as 39 percent and still capture 51 percent of the vote. With this 15 percent bloc of the evangelical Christians in his pocket, Reagan was able to lower marginal tax rates to 28% and still capture the election. Roe lowered the marginal tax rate from at least 39 percent- perhaps even 70 percent to 90 percent- to 29 percent to 34 percent.
Most pro-investment tax cutters are pro-choice. They endorse the pro-life agenda for no other reason than to bring their minority bloc of voters to power. Because of this endorsement, Republicans lose a small number of pro- investment tax cutters to the Democrats.
From Unintended Consequences by Edward Conrad
The political parties are merely coalitions with different interests that unite for a political goal. Many will vote for the GOP who stand against their social platform, because they stand against the reckless Democratic handling of the economy more. Depending on the the key issues at the time of the election these coalitions can shift, sometimes dramatically.
While this alliance has propelled a more fiscally sound policy forward, and in spite of the 2008 financial collapse, we remain on a sounder economic footing than Europe – it has come at the costs of some division within the GOP. Like the issue of abortion, the current controversy over gay marriage will also serve to galvanize evangelicals, but I do not see that it changes the balance any more than has already existed. This alliance still serves to limit tax increases.
The growing acceptance of the secure right to an abortion (with limitations) and the growing acceptance of gay marriage also provides a strong coalition partner to the Democratic Party. The voters may tolerate the less progressive stand of the GOP on these issues if they see an advantage in their management of the economy. If they can not distinguish a sharp difference on their economic policies then they will choose where they do see a difference and these social issues could hurt the GOP.