When Republicans began questioning President Obama’s birth certificate four years ago, it seemed at first like a petulant reaction to a lost election, a flush of nativist and racist anger that would diminish over time. But the preposterous charges never went away. As this election cycle shows, many in the Republican Party continue to see the president as the center of a broad and malevolent liberal conspiracy to upend the truth.

To live and seethe in that world of conspiracy theories means rejecting any form of objective reality. When unemployment numbers make the administration look good, they are obviously “cooked.” When poll numbers put Mr. Obama ahead, they are skewed. Birth certificates are forgeries. Safety-net programs are giveaways to supporters. Health insurance reform is socialism. And campaign donation disclosure is antibusiness.

It’s an upside-down version of life, and it is not innocuous. When desperation leads political critics of the president to discredit important nonpolitical institutions — including the Census Bureau, the Bureau of Labor Statistics, the Federal Reserve and the Congressional Budget Office — the damage can be long-lasting. If voters come to mistrust the most basic functions of government, the resulting cynicism can destroy the basic compact of citizenship.

Last week, the Labor Department reported that the unemployment rate had fallen to 7.8 percent, depriving Mitt Romney of his standard talking point that the rate had never been below 8 percent during Mr. Obama’s term. No one expected Republicans to celebrate a positive trend for the country, but almost immediately the anchors on Fox News and the editors of right-wing Web sites saw something more sinister: a conspiracy, led by the Obama campaign, to manipulate the numbers to make the president look good a month before the election.