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.