There was a time when I was unconvinced of the case that greenhouse gases were causing the planet to warm and that action was needed to curb them. I'm not one to jump to conclusions on such an important matter. But over time, I noticed something fishy. The people who began by rejecting the case kept changing their story.
First, they said the planet was not getting hotter. Then they said it might be getting hotter but not because of carbon dioxide. Then they said that maybe the increase of carbon dioxide in the atmosphere was causing it but that it was a good thing. Then they said that even if it's a bad thing, it would be costly or futile to take remedial action. At each stage, they devised a new argument.
What didn't change was their unshakable commitment to doing nothing. They didn't consider the evidence and then sort through it to reach a logical conclusion. They reached a conclusion and then found ways to justify it no matter what. Most of these people, as it happens, were Republicans.
Psychologists have a term for this approach: motivated reasoning. As Jerry Taylor, president of the Niskanen Center, a moderate think tank, has explained, it "is the act of deciding what you want to believe and using your reasoning power, with all its might, to get you there."
It's on display at any athletic contest, where a referee's decision against the home team will draw boos, even if it is obviously correct. Fans want their team to win, so they dispute any call that hurts their team. If sports fans didn't engage in motivated reasoning, they would boo bad calls against the opposing team.
This tendency is what novelist Upton Sinclair was referring to when he wrote, "It is difficult to get a man to understand something, when his salary depends upon his not understanding it."
The same phenomenon is on view in the Senate impeachment trial. To anyone who started out with an open mind, it would be clear that Donald Trump used military aid and other means to pressure the president of Ukraine to take steps to harm a prospective opponent, Joe Biden.
It would be clear that the president's efforts defied Congress and had nothing to do with combating corruption. It would be clear that he has abused his powers, lied incessantly about his actions and gone to exceptional lengths to prevent Congress and the public from learning the full story.
But Republicans refuse to admit the obvious, preferring to dissemble, smear the accusers and concoct fraudulent rationales for what Trump did. They have an interest in Trump's survival, so they make — and may even believe — whatever claims are necessary to protect him.
This is not how Democrats proceeded on impeachment. They waited for the Mueller report and, when it arrived, decided that it didn't provide a sufficient case to remove Trump. Nancy Pelosi stoutly resisted the calls from some members for impeachment.
Only after the Ukraine extortion scheme came to light did she and most of her members decide they had no choice. In making the case against Trump, they have relied on proven facts and reasonable inferences, not the bald deceptions and disinformation his supporters employ.
But motivated reasoning is an old human tendency. The question is: Why has it become so dominant in the Republican Party? One reason lies in the ideological sorting of the two parties.
There used to be conservative Democrats and liberal Republicans. The overlap of views moderated partisanship because liberal Democrats needed the help of liberal Republicans, and conservative Republicans sometimes worked with conservative Democrats.
As each party became ideologically narrower, the pressure to follow the party line came to predominate. The need to persuade doubters within the party largely vanished. Truth has often been a sad casualty.
The Trump presidency has forced Republicans to choose between seeing what's staring them in the face and finding ways to justify his worst impulses. They have chosen the latter, even when he has abandoned longstanding GOP policies - on Russia, Ukraine, NAFTA, North Korea, immigration, spending and more. Trump is now the Republican Party, and Republicans will go where he takes them, even if it means denying reality. And Fox News will help.
More than a century ago, a titanic political leader said, "There is only one truth: what profits my opponent hurts me, and vice versa." That has become the operating principle of Republicans. For these onetime anticommunists to follow the example of Vladimir Lenin only highlights how far they have come.
Steve Chapman blogs at http://www.chicagotribune.com/news/opinion/chapman. Follow him on Twitter @SteveChapman13 or at https://www.facebook.com/stevechapman13. To find out more about Steve Chapman and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.