The Huckabee boomlet has been stunningly swift, even surprising those who say they saw it coming many weeks ago.

The source of Huckabee’s appeal to conservative and evangelical Republicans is pretty simple. He’s not a flip-flopping Mormon or a pro-abortion-rights, pro-gay-rights, pro-gun-control adulterer. And he’s never put his name on a bill with Sen. Edward Kennedy (D-Mass.) or Sen. Russ Feingold (D-Wis.), or lambasted the Christian right.

In a sense, Huckabee is the second coming of former Sen. Fred Thompson (R-Tenn.), who now seems about as relevant as a typewriter at a bloggers’ convention.

Thompson, of course, was conservatives’ first great hope of keeping the Republican Party on a course set out by Ronald Reagan more than a quarter century ago. If you recall, he was going to be the “new Reagan.”

Thompson shot up in the polls even before Republican voters had given him a good look. They didn’t know much about him other than he filled a role they wanted filled.

When the real Thompson seemed less energetic and appealing than the imagined Thompson, Republicans fell out of love with him. They were still looking for someone not named Giuliani, Romney or McCain when they found Huckabee, a quirky (diet- conscious former pastor) Southerner who talks in a conversational style, emphasizes conservatism and common sense, and seems to lack the flaws other Republicans have.

Huckabee always looked like the conservative alternative, and he is now filling that role. His strength in Iowa and South Carolina, but not New Hampshire, suggests that he is appealing to social conservatives in general and evangelicals in particular.

But let’s be clear about Huckabee’s support: While he has surged primarily because he isn’t one of the other guys, he’s in a far stronger position than Thompson was when the Tennessean was riding his wave.

Thompson was rising in the polls when he was merely an idea and hadn’t spent a day on the stump as an active candidate. Huckabee has been in Iowa for months, finishing second in the state’s straw poll and participating in a seemingly endless number of televised debates.

Iowans have seen Huckabee and been impressed by his debate performances and down-to-earth style and message. So, unlike Thompson, Huckabee has some definition and voters have warmed to him over the months.

For the past month or more, former Massachusetts Gov. Mitt Romney’s camp has been discussing how to deal with what many inside the campaign saw as the growing threat from Huckabee. Instead of attacking Huckabee when the Arkansan started to make his move, which surely would have entailed risks but might have blunted the surge, Romney consultant Russ Schriefer and campaign manager Beth Myers decided to sit tight. Recent polls have forced a change of strategy.

Romney can survive a competitive loss in Iowa if he can go on to win five days later in New Hampshire. But losses in each of the first two contests would all but eliminate him.

Iowa conservatives probably don’t know as much about Huckabee as they think they do. In the next month, they will learn more about his support for additional taxes and spending, his moderate position on illegal immigration, his role in the release of a convicted rapist who went on to sexually assault and murder a woman in Missouri, and his wedding registries at two department stores that were created two decades after he was married so that he could receive gifts as he exited the governor’s office.

Huckabee doesn’t have elaborate campaign organizations in place after Iowa, but it’s not all that difficult to construct a scenario that would allow him to be one of the two Republicans left standing after South Carolina, along with former New York Mayor Rudy Giuliani. And that means he can’t be dismissed as a contender. In fact, nobody can. Certainly not Sen. John McCain (Ariz.). Not even Thompson.

Still, the Huckabee surge seems odd, very odd, on at least a couple of levels.

First, journalists like Huckabee and say he sounds “reasonable.” Yes, he’s socially conservative, but they like his views on immigration, taxes and government, as well as his sense of humor and appreciation for popular culture. They find him charming. For conservatives who see most journalists as the enemy, those words are faint praise.

Second, and of far greater importance, Huckabee has zero experience and credibility on foreign policy and national security — the top issue to many Republicans since the Sept. 11, 2001, attacks, and the one issue that the Republican nominee may be able to use to hold onto the White House.

With wars going on in Iraq and Afghanistan, Russia looking like the old Soviet Union, the president of Venezuela sounding like a crackpot and terrorist forces still looking to inflict pain on the United States and its allies, defense and national security issues are certain to be important in next year’s election.

Given the importance of these issues, does anyone think Huckabee has the gravitas, experience and credentials to carry an argument to Democrats on foreign policy? It’s hard to see how he could make Sen. Barack Obama’s (Ill.) inexperience in foreign affairs an issue or challenge Sen. Hillary Rodham Clinton’s (N.Y.) credentials to lead the war against terror.

And if electability truly is an important issue for the GOP, Huckabee could be a disaster. While some have argued that he could hold conservatives on abortion and civil unions and appeal to swing voters and even Democrats on immigration, spending and domestic priorities, it is more likely that he would lose conservatives on taxes, spending and immigration and alienate moderates and Democrats on social issues.

Stuart Rothenberg is editor of the Rothenberg Political Report.