Over the past fifty years the political parties have realigned demographically and ideologically. In general, conservative groups moved towards the Republican Party and liberals have become Democrats. For example, the Dixiecrats switched from the Democratic Party to the Republican Party and Evangelical Christians became politically active and joined the Republican Party; while conservationists and "good government" reformers abandoned the Republican Party for the Democratic Party. Conservative Democrats and liberal Republicans no longer exist in any numbers. Thus, today there is a sharp ideological divide between the parties, making it difficult to find common ground on issues such as climate change, health care policy, gun control, immigration, or same-sex marriage. But another difference has also arisen between the two dominant political parties in the United States: an epistomological one. Democrats, who in general seek to change the future, are increasingly drawn to science and economic analysis, while Republicans, who wish to preserve or return to what they value in the past, are more and more likely to depend upon various forms of magical thinking. Some examples follow.
The difference in analytical styles is sharpest on the question of climate change. The Democratic position is almost entirely dependent on scientific research. No average citizen has sufficient experience or expertise to detect climate change; even if we think it's warmer than it used to be, without science we would be at a loss to explain why it was happening. But scientists are confident that the planet is warming; that this phenomenon is due to increasing concentrations of man-made carbon emissions in the atmosphere; and that if we do not halt this process it will result in massive destruction and suffering around the world.
In general, Democrats accept this narrative as true because of their willingness to rely on science. Republicans reject it, preferring to base their beliefs upon what is consistent with their view of the proper role of government as well as a desire to preserve existing allocations of resources and wealth. If one believes unreservedly in limited government, then anything that would necessitate massive government intervention cannot possibly be true. And if one's livelihood (or the lifeblood of one's political party) is based upon the coal industry or oil and gas, then one has a strong incentive to call climate change a "hoax"; or to deny that it is being caused by human activity; or to throw up one's hands and say that there is nothing that can be done; or even to imagine that another ice age is imminent that will make global warming irrelevant, if not a benefit.
The same was true of the parties' positions on the Affordable Care Act. The law's complicated structure of mandated and subsidized private health insurance was based entirely on the forecasts and predictions of economists. The statutory scheme has hundreds of moving parts; each time one of the proposed law's provisions was changed, it affected the predicted outcome in complex ways. The goals of the law were ambitious; it was intended to expand access to health care, to slow the pace of inflation in the health care industry, and to improve the quality of care. Now that it is in effect the law is working on all three fronts, thank goodness. I studied the bill intently as it moved through Congress, and wrote a data-heavy book about the projected economic impact of it just after it was enacted into law. But ultimately I, like other Democrats, was relying on the expertise of economists who said that it would probably work. As with climate change, Republicans denied that it would work; again, not because they had evidence to the contrary, but because the proposed law conflicted with their beliefs about the proper role of government. The proof of this is that to this day the Republican Party has not proposed a plan of universal health care. In the face of overwhelming proof to the contrary they claim that the Affordable Care Act is a failure. Ideologically, I suppose it is a failure in their eyes. But in the real world it has exceeded expectations in expanding access, reining in costs, and improving the quality of care that people actually receive.
Gun control is yet another example. Democrats oppose the widespread availability of deadly firearms because 30,000 Americans are killed and over 100,000 are wounded every year by guns. Democrats want to craft wise and fair gun control policies in order to reduce this carnage. Republicans do not simply oppose gun control; they oppose any and all scientific research about the availability and use of guns! This is above all a public health issue, yet the Centers of Disease Control is forbidden by law from conducting scientific research on gun violence! Democrats want reliable, detailed information upon which to base our policies. Republicans don't want the facts. For them it is sufficient to rely upon the myth, promoted in virtually every Western and detective story, of "the good guy with a gun."
Finally, we see the same epistomological divide on the question of same-sex marriage. In the scientific realm in study after study sociologists, psychologists, social workers, and physicians have determined that homosexuality is not a deviation but rather simply one aspect of normal human behavior. There is no difference between people in same-sex unions and opposite-sex unions, either in their love for each other or their ability to raise children. Science tells us what many of us have discovered in our daily lives. People are people, and sexual orientation has no correlation to the ability to form strong families or to do anything else for that matter. There is simply no rational reason for the law to discriminate against gay and lesbian individuals or couples.
But the absence of rational proof has proven to be no impediment to most members and most leaders of the Republican Party. They still oppose same-sex marriage - and many go further and want to reinstate laws that would discriminate against gays and lesbians in the military and to enact laws that would permit private businesses to discriminate against their gay and lesbian customers and employees. The reason that Republicans invoke for their opposition to marriage equality is almost always "religion." Not science. Not reason. In their eyes gays and lesbians are not equal simply because God has told them that these people are not equal, and laws that treat them as equal violate conservatives' rights to "religious liberty."
Our political parties are deeply divided. The racial and ideological differences make it difficult enough to reach acceptable compromises. But the differences between the parties run much deeper. Democrats and Republicans have different ways of separating truth from falsity and different ways of telling right from wrong. Those philosophical differences make it difficult to even have a rational discussion with someone on the opposing side.