It is now being reported that Donald Trump is likely to play a "surprise" part on the first day of the Republican National Convention in Tampa, Fla. -- perhaps, some speculate, in a comedy bit involving the firing of a Barack Obama impersonator. "The role, like Mr. Trump," says a Trump spokesman, "is unique and will be memorable for all those in attendance at the convention and those watching around the country. Stay tuned."
The appearance is further evidence of one of the oddest flirtations in American politics. Trump and Mitt Romney appeared together at a Las Vegas fundraiser in May. The Romney campaign raffled off a meal with the pair as a reward for campaign donors.
Romney supporters tend to be perplexed by his ties to Trump but dismissive of their importance. No one is likely to confuse the members of a couple this odd. On the plus side, this connection may help unbutton Romney's public image. Add a little pop culture sizzle. Bring in some extra cash.
All of these justifications would make sense if we were talking about Kim Kardashian, who is famous merely for her fame. But Trump is also famous for spreading conspiracy theories. He is the nation's highest profile "birther," who sent investigators to Hawaii to uncover proof of Obama's duplicity. Finding none, he moved on to the sinister mystery of the president's unreleased college transcripts. Turning his attention from politics to medicine, he has asserted that multiple vaccinations cause babies to be "different," based on this evidence: "I've known cases." When informed that most physicians disagree, he responded: "I know they do. ... I couldn't care less."
Set aside that vaccine skepticism is the medical equivalent of encouraging children to play in traffic. Trump represents not merely wealth and brashness but an attitude toward authority and knowledge. He has developed a standing among some populist conservatives by arguing that mainstream information is fundamentally biased, that public officials are engaged in elaborate deceptions, and that only a courageous few can understand and uncover the alarming reality. Politics, in this view, is not the contest of ideas; it is the exposure of a plot. It matters little if hard evidence is nonexistent, which is taken as further evidence of the plotters' diabolical sophistication.
This isn't new in American history, but that doesn't make it less damaging. In "Voodoo Histories," an entertaining demolition of modern conspiracy theories, David Aaronovitch argues that tolerance for conspiracy thinking amounts to a kind of "relativism," which "doesn't care to distinguish between the scholarly and the slapdash, the committed researcher and the careless loudmouth, the scrupulous and the demagogic." Everyone becomes entitled to their own "alternative narratives," at the expense of rationality, earned authority and objectivity. And conspiratorial narratives are often divisive and disturbing.
That is certainly true of presidential conspiracy theories -- that Bill Clinton ordered a series of murders, or that George W. Bush was complicit in the attacks of Sept. 11, 2001, or that Obama illegally holds the presidency through deception. These charges are designed to delegitimize presidents. Instead of being opponents with different views, they become aliens or oppressors, unworthy of power and respect.
This brings the fracturing of America to a new level. It is more difficult to unite people following an election when a significant portion of political activists, based on the finest Internet sources, are convinced that a president is a fraud or a monster. Once the narrative of conspiracy is accepted, unity becomes a vice. Divisions and contempt become permanent.
A few official campaign appearances by Trump do not imply a full embrace of birtherism by Romney or the Republican Party. But it is not healthy to take even a little bit of this hemlock. Trump's appearance at the Republican convention represents a disturbing tolerance for disturbing ideas. What does it say about the modern GOP that the leading advocate of the theory that Obama is Kenyan is on the convention schedule, while the leading advocate, say, of mainstream climate science would risk being booed off the stage?
And there is a cost to Romney himself. The mainstreaming of Trumpism, in a small but significant way, undermines the authority and standing of the office Romney seeks and further divides the nation he hopes to govern. And if Romney uses part of his convention speech to confront the Obama campaign's relentless negativity and nastiness -- which he should -- his opponents will have a simple riposte: Your convention had Donald Trump.
Email Michael Gerson of The Washington Post at email@example.com.