By Jonathan Zimmerman

So here's a question for Scott Brown as he prepares to enter the U.S. Senate: Do you believe President Obama was born in the United States?

And here's why it needs to be asked: Many "Tea Party" activists who backed Brown think Obama was born overseas, which would make him constitutionally ineligible to be president. Somehow, these folks insist, the most closely observed man on the planet managed to keep his origins a secret from everyone - except them.

In short, they're paranoid.

Paranoia runs deep among the Tea Partiers, who happily took credit for Brown's upset victory in Massachusetts last month. They're a diverse, amorphous lot, united mainly by antipathy toward Obama's health-care proposals. But a significant portion also think the president was born abroad and is a closet Muslim. "I do not want a president that bows to the king of Saudi Arabia," a Tea Party leader told a rally in Pennsylvania last year.

So does Brown buy any of this? Do other GOP members of Congress? In the balance is the soul of the Republican Party, which needs to decide whether it will call out the crazies in its midst.

The party faced the same dilemma in 1964, when historian Richard Hofstadter wrote his now-famous essay "The Paranoid Style in American Politics." Hofstadter warned that a ragtag band of conspiracy theorists - including the far-right John Birch Society - were taking over the GOP and rallying behind Barry Goldwater in that fall's presidential race. Birchers founder Robert Welch had claimed President Dwight Eisenhower was a "dedicated, conscious agent of the Communist conspiracy."

The Birchers stood in a long line of American paranoids, Hofstadter argued, from the anti-Masons of the antebellum era to the anti-flouridationists of more recent vintage. "I call it the paranoid style," he wrote, "simply because no other word adequately evokes the sense of heated exaggeration, suspiciousness, and conspiratorial fantasy that I have in mind."

And no word better describes today's "birthers," who have even found a foothold in Congress. In a tacit endorsement of the movement last year, 10 Capitol Hill Republicans sponsored a bill to require future presidential candidates to produce their birth certificates.

This fall's elections could bring still more birthers into the fold. In a GOP primary today, for example, birther Andy Martin is competing for the Illinois U.S. Senate seat once held by Obama himself.

Paranoia has often infected the American left as well as the right. Most recently, so-called "truthers" claimed the often incompetent Bush administration somehow coordinated the 9/11 attacks with perfect precision and without anyone (except the truthers!) finding out.

But you won't find any truthers in Congress. Fed by Obama's ascent, right-wing paranoia has a lot more traction right now. That's why Republicans need to read these people out of the party as soon as possible.

That's what they did in the early 1960s. Even as Hofstadter was railing against the Birchers' incursions into the Goldwater camp, party operatives were working to marginalize them. Following a 1962 meeting with Goldwater, National Review editor and conservative stalwart William F. Buckley published a long article denouncing the Birchers as "paranoid" and deceitful.

"The underlying problem is whether conservatives can continue to acquiesce quietly in a rendition of the causes of the decline of the Republic and the entire Western world which is false," Buckley wrote.

That's also the problem for Brown and the rest of today's GOP. Not everyone who voted for Brown is a member of the Tea Party movement, and not every Tea Partier is a birther. But plenty of them still indulge these fantasies, and Republican leaders have acquiesced quietly - or, sometimes, loudly - in them.

They might consider taking a page from Goldwater, who followed Buckley's editorial with a letter of his own. Goldwater was reluctant to criticize the John Birch Society, which was making big strides in his native Arizona. But he did it anyway because it was the right thing to do.

"We cannot allow the emblem of irresponsibility to attach to the conservative banner," Goldwater wrote, adding that the Birchers' Welch was "far removed from reality and common sense."

The same goes for the birthers: They're paranoids in the not-so-grand American tradition, and they're pulling the party down with them. The only question is whether honest Republicans will have the guts to say so.

Jonathan Zimmerman teaches history at New York University, lives in Narberth, and is the author most recently of "Small Wonder: The Little Red Schoolhouse in History and Memory." He can be reached at jlzimm@aol.com.