Theodore Roosevelt once called William Howard Taft “a fathead with the brains of a guinea pig.”

Harper’s Weekly once described Ulysses S. Grant as “a drunken Democrat dragged out of the Galena (Ill.) gutter.”

Which was positively charitable compared to the magazine’s take on Abraham Lincoln, “a filthy story-teller, despot, liar, thief, braggart, buffoon, usurper, monster, ignoramus, old scoundrel, perjurer, robber, swindler, tyrant, field-butcher, land-pirate.”

So perhaps we can dispense with the notion that incivility is somehow new to American political discourse.

And as Eric Burns illustrates in his book, Infamous Scribblers: The Founding Fathers and the Rowdy Beginnings of American Journalism, slanted reporting is no modern innovation, either.  To the contrary, Colonial-era papers were not simply open in their support or opposition to a given politician or policy, but often came into being for that express purpose.  As the editor of a paper in Danbury, Conn. put it two centuries ago, “A despicable impartiality I disclaim.”  So no, bias is not new.

And yet …

It is difficult to escape a nagging sense that something fundamental has changed in American journalism, that the aggressive but fair kind of reportage many of us grew up yearning to emulate – Cronkite, Murrow, Woodward, Bernstein, Pyle – has been superseded by something coarser and much less concerned with truth.  Consider the tale of Shirley Sherrod.  As even residents of the rainforest must know by now, she was the black Agriculture Department employee who was depicted as a racist in a video posted by blogger Andrew Breitbart.  She had been fired from her job and nationally reviled before the truth came out: the video had been selectively edited and Sherrod was actually the opposite of a racist.

And there you have it, the thing that’s new: not the libel, not the bias, but the reach, the ability of a single individual, lacking a newsroom or traditional distribution machinery, to elbow his way into the national discourse, and in this case, to cost a woman her reputation and livelihood, through the simple expedient of a shameless lie.  A lie, Mark Twain once observed, can get halfway around the world while the truth is still pulling on its pants.

Not to put too fine a point on it, but Twain died in 1910, decades before CNN was founded and the world wide web became part of our daily lives.  If lies moved that fast in his era, their speed is incalculable now.

Therein lies the challenge.  Where once we were all restricted to the same body of verifiable facts upon which to base our arguments and disagreements, the very ubiquity of untruth has removed that necessity.  I am not required to hear – much less credit – any facts I don’t like.  In the 21st century, I choose my beliefs first, then am provided with “facts” to support them.

The result is that it becomes literally impossible to have reasoned debate or even argue effectively, because we begin with no assumptions in common.  You have your “facts” and I have mine and never the twain shall meet.

Both major political ideologies have exploited this gap, as witness the liberals who use “facts” to insist no airplane struck the Pentagon on Sept. 11, 2001.  But it is undeniably conservatives who have done the most to exploit the gap – not simply by peddling  birther canards, but also by constructing what amounts to a social isolation chamber to prevent contamination from competing facts.

It began with conservative cable news and conservative radio.  It has been followed by a conservative alternative to the Bible, a conservative alternative to Wikipedia, a conservative alternative to the AARP, a conservative alternative to Webster’s Dictionary, a conservative alternative to YouTube and – you can’t make this stuff up – even a conservative alternative to ice cream.

It is not too much to say that we are witnessing an act of intellectual secession.

The irony of the age, then, is this: the humble newspaper, beset by financial challenges, fighting for its life, is the one medium that has proven relatively resistant to this intellectual partitioning.  Maybe the partitioners just don’t care enough about newspapers to subvert them; one wonders if Andrew Breitbart even knows such a thing as a “newspaper” exists.

Whatever the cause, the effect is that in what some fear are their waning days, newspapers assume a paradoxical significance.  Because they do not deal in designer facts, because they still try and occasionally succeed, in getting it right, in telling the story fully and fairly, they become the closest thing American political discourse has to an honest broker.  That function has seldom been more critically important than it is now.

A nation where everybody acts upon his or her own “facts” is a nation pulling apart.  By behaving as if truth is not multiple choice, as if facts are knowable and knowing them matters, newspapers pull us together.

Some days, it feels as if they are the only thing that does.

Leonard Pitts Jr. is a Pulitzer Prize winning syndicated columnist.