[Gil Troy, a professor of history at McGill University and visiting scholar at the Bipartisan Policy Center in Washington, is the author of Leading from the Center: Why Moderates Make the Best Presidents and The Reagan Revolution: A Very Short Introduction.]

Barack Obama's election to the presidency was supposed to usher in a new, more mature era of race relations, but it could not evoke nirvana. There's a growing chorus complaining that this summer's hostility to his stimulus package, to his health-care reform and to Mr. Obama himself is racist.

“I think it's based on racism. There is an inherent feeling among many in this country that an African-American should not be president,” former president Jimmy Carter said, clearly forgetting the euphoria when Americans elected a black president.

New York Times columnist Maureen Dowd said she heard “an unspoken word in the air” when Republican Representative Joe Wilson shouted “You lie!” during the President's speech to Congress last week: “You lie, boy!” She also located Mr. Obama “at the center of a period of racial turbulence sparked by his ascension.” In fact, Mr. Obama is at the center of a political storm sparked by his leadership – as all presidents have been.

American politics is a contact sport. The long, rich tradition of American centrism does not negate the equally long colorful tradition of American mudslinging and partisanship. It is unfair and itself divisive to impute racial motives to Mr. Obama's opponents without evidence. The shrill opposition reflects the high stakes surrounding the current debate, Americans' enduring ambivalence about big government and the ugly way modern politics plays out in the media, within the blogosphere and on the streets.

Mr. Obama is controversial because he is seeking big changes. He's no Bill Clinton in his second-term incarnation, focusing on minor policy “Band-Aids” such as the “V-chip” and school uniforms. Mr. Obama wants to be a transformational president like Ronald Reagan. During the transition, faced with the unexpected economic crisis, Mr. Obama read books about how Franklin Roosevelt re-engineered the U.S. economy. Headlines celebrating “Franklin Delano Obama” launched Mr. Obama's ambitious first hundred days. Spending nearly a trillion dollars to stimulate the economy, taking over the U.S. auto industry, and now trying to solve the perennial health-care riddle – while protecting America and seeking world peace – are sweeping goals. No wonder there's pushback.

The conservative counterattack is particularly intense because Mr. Obama seems to forget that Americans have mixed feelings about big government. There's a strong individualistic streak in American thought. Every major jump in the government's mandate has encountered fierce resistance. Conservatives denounced FDR as a Mussolini and even a Hitleresque dictator.

In 1993, Hillary Clinton was shocked at the vitriol directed her way when she led health-care reform efforts. The Clintons, in fact, endured far more abuse than Mr. Obama has – so far. The Clintons were accused of drug-running, murder, faked suicides, financial corruption, rape and cover-ups galore. After his impeachment, Mr. Clinton lamented Republicans' descent into the “politics of personal destruction.”

Mr. Clinton and his fellow Democrats suggested these attacks were a conservative Republican tic. The implication then – as now – was that liberals disagreed as rational, reasonable human beings; conservatives were harsh, hysterical, character assassins.

Unfortunately, the loony left can be as vicious as the ranting right. In the 1980s, Mr. Carter and the Democrats called Mr. Reagan a war-mongering racist who would deprive blacks of civil rights while bumbling into nuclear war. One of the Democratic Party's grand old men, Clark Clifford, called Mr. Reagan “an amiable dunce.” Respected liberal writer Garry Wills called him “Mr. Magoo.”

George W. Bush endured even more vicious attacks. Mr. Carter himself was one of many Democrats who said America's leaders lied in the buildup to the Iraq war. During the 2004 campaign, an Internet ad compared Mr. Bush to Hitler. Bushophobia became so intense that critics often seemed more disgusted by Mr. Bush than by Saddam Hussein or Osama bin Laden. “There is something profoundly wrong when opposition to the war in Iraq seems to inspire greater passion than opposition to Islamist extremism,” Senator Joe Lieberman, [then] a Democrat, said in 2007.

Vice President Richard Cheney was even more hated, and routinely compared to Darth Vader. Much of this enmity stems from the ever-accelerating news cycle, the blogosphere's nastiness and Americans' ability to speak, text and listen only to those with whom they agree.

Mr. Obama promised to lower the volume – acknowledging how shrill politics was under Mr. Clinton and Mr. Bush, two white presidents. Obama supporters should not be shocked that Republicans are attacking Mr. Obama as vehemently as Democrats attacked his predecessor.

And it is dishonest for Mr. Carter, Ms. Dowd and others to play the race card, implying that anyone who dares disagree with Mr. Obama's health-care plan or stimulus package is a redneck. American politics needs a different tone – these delusional, demagogic, racial recriminations only make things worse.