WASHINGTON — Before there was the tea party to define the phrase “far-right fringe,” there was Rick Santorum. He’s a nice-guy zealot who should never be allowed anywhere near the Oval Office.

It’s understandable that progressives would be tempted to cheer Santorum’s sudden rise as a viable candidate for the Republican nomination. The likely nominee, Mitt Romney, would love to be able to modulate his rhetoric and begin running a more centrist campaign that could appeal to independents in November. But if Santorum continues to pose a threat, Romney will likely have to move even further right — ceding valuable political ground to President Obama.

And if Santorum somehow manages to win the nomination, he will be easier for Obama to beat than Romney. I mean, Obama beats him easily. Doesn’t he?

But I know there’s no such thing as an airtight guarantee, and that’s why those welcoming the Santorum surge for Machiavellian reasons should be careful what they wish for.

I mentioned that he’s a nice guy. Unlike Romney, Santorum is perfectly at ease chit-chatting with strangers. He makes eye contact, engages the person he’s talking to and gives the impression that he’s speaking from the heart, not from a position paper. He seems genuine.

The problem is that his views are genuinely extreme and, in some instances, patently offensive. He is a cultural warrior who has equated same-sex marriage with polygamy, pedophilia and bestiality — and argued that gays and lesbians should not serve openly in the military because “they’re in close quarters, they live with people, they obviously shower with people.”

Don’t worry: Santorum says he doesn’t have a problem with homosexuality, just with “homosexual acts.” So, all you gay people out there, just go sit in a corner. And no touching.

For heterosexuals, Santorum wants to end federal funding for contraception. Yes, he opposes birth control. Contraception, he said in October, is “not OK” because it gives people “a license to do things in a sexual realm that are counter to how things are supposed to be.” Thankfully, no one asked the obvious follow-up question.

Santorum also has linked the projected Social Security shortfall to rampant contraception — basically, birth control means fewer babies who would grow up to be workers whose payroll taxes would support the hordes of retirees who were born in simpler, purer times, when condoms were kept behind the counter and dispensed only at the whim of a stern and judgmental pharmacist.

Santorum is implacably opposed to Obama’s health care reforms. Among other objections, he has said that insurance companies should continue to have the right to deny coverage — or charge more — for individuals who have pre-existing conditions. “I’m OK with that,” he said last month.

On the other hand — and this is what makes him potentially a tougher opponent for Obama than many people think — Santorum, unlike the other Republican contenders, has a discernible social conscience. During the debates, he has spoken eloquently of the pain that blue-collar families are feeling because of economic dislocation. His platform includes a plan to give preferential treatment to the manufacturing sector — according to free-market dogma, a forbidden exercise in “picking winners and losers.”

Santorum’s working-class background and manner might give him an appeal to Rust Belt voters that Romney could never match. And while Santorum lost his last election by a landslide, no one can doubt that he’s a skilled politician. A couple of months ago, he was driving himself to campaign stops in order to save money. Look where he is now.

And look where we would be if somehow he got elected: quite possibly, at war with Iran.

I do not say this lightly. With the exception of Ron Paul, the Republican candidates have competed to see who can be most hawkish on Iran’s nuclear program. Santorum wins, hands down. He has said flatly that unless Iran agrees to open its nuclear facilities to inspection and begins to dismantle them, as president he would order military strikes. In fact, Iran is already under nuclear inspection, but Santorum seems not to care. He has said he believes an attack by Israel or the U.S. is probably inevitable.

It’s quite difficult for a president to change the nation’s culture. It’s quite easy for a president to start a war. Yes, the GOP’s clown-car nomination battle is a source of amusement. The prospect of a Santorum presidency, though, is a source of alarm.

Eugene Robinson’s email address ieugenerobinson(at)washpost.com.