Former Utah governor Jon Huntsman may be trailing the pack in the Republican presidential primary, but he is a leader in one important regard: Unlike his colleagues, Huntsman has refused to sign any of the special interest pledges that are increasingly turning political office into an ideological straitjacket.

Huntsman has been joined by Mitt Romney and Tim Pawlenty in rejecting one particularly odious pledge — the Marriage Vow put forward by the Family Leader, a conservative values group run by Bob Vander Plaats, a power player in the Iowa Republican caucuses. Those who sign the Family Leader pledge — including Rep. Michele Bachmann of Minnesota and former Pennsylvania senator Rick Santorum — promise to oppose “intimate unions which are bigamous, polygamous, polyandrous, same-sex, etc.”

Although the pledge is largely devoted to the Godzilla-like terrors associated with all things gay and lesbian, it doesn’t stop there.

It also demands that signatories oppose the deployment of women in forward combat roles and commit to protect women and “the innocent fruit of conjugal intimacy” — otherwise known as children — “from seduction into promiscuity” and other instances of “stolen innocence.”

Bachmann received a round of bad press over the pledge’s assertion — since modified — that certain innocent fruit of conjugal intimacy had been better off as the fruit of slaves.

“Slavery had a disastrous impact on African-American families, yet sadly a child born into slavery in 1860 was more likely to be raised by his mother and father in a two-parent household than was an African-American baby born after the election of the USA’s first African-American president,” the pledge stated.

(As with the apposition of the words “holocaust” and “but,” the combination of “slavery, yet” is a sure sign that you’ve run off the rails.)

Yet critics who argue that Bachmann lacks the judgment to be president are missing a key point.

If Bachmann, a serial pledge signer, were to become president, she wouldn’t have a prayer of thinking for herself. She’d be locked into special-interest pledges for every occasion.

She also has signed the Susan B. Anthony List pro-life pledge, which imposes an anti-abortion litmus test on virtually all of a president’s federal appointments, and the Cut Cap Balance pledge, a pet project of Sen. Jim DeMint, a South Carolina Republican, and former House majority leader Dick Armey.

The Cut, Cap and Balance bill, which the House debated last week, proposes to cut federal spending in the next fiscal year by $111 billion, eventually cap spending at less than 20 percent of gross domestic product, amend the Constitution to require a balanced budget every year and make it almost impossible to raise taxes.

As policy, it has no chance of ever being enacted. But in order to curry favor with its ideological champions, including the powerful anti-tax group Club for Growth, which eagerly attacks Republicans who don’t fall in line, Republican presidential candidates have pledged to support the fantasy.

Democrats have their own pledges. Naral Pro-Choice America, the abortion-rights organization, demands that candidates fill out a written questionnaire. The same is true of Emily’s List, which requires its candidates to possess two X chromosomes, a pro-choice position and a viable chance to win election as a Democrat. When two Emily’s List-backed senators, Blanche Lincoln of Arkansas and Mary Landrieu of Louisiana, supported a Republican bill to ban late-term abortion, they promptly lost lucrative support.

The mother of all pledges is Grover Norquist’s Tax Protection Pledge. First issued in 1986, it has been signed by countless Republicans over the past quarter century, including 236 current House members and 41 current senators. Yet Norquist’s success is perhaps the best argument against rigid pledges, which infantilize officials, giving them no leeway to exercise judgment.

Republicans had a miracle deal in their grasp earlier this month, but like children they rejected the ice cream cone they would have otherwise devoured — $3 trillion in federal spending cuts — because it had the wrong kind of sprinkles on top — $1 trillion in revenue increases.

In effect, Republicans passed on the conservative deal of the century — huge spending cuts with no increase in tax rates — in part because they had signed pledges to Norquist, who views every increase in government revenue as a personal affront.

To enforce his pledge, Norquist threatens free-thinking Republicans with political ruin, a threat he backed in 2010 with $7.5 million in campaign spending. But where are all the dead bodies? Norquist did help to defeat a few state legislators last year, along with California Lt. Gov. Abel Maldonado, who had offended Norquist by supporting Gov. Arnold Schwarzenegger’s 2009 budget.

Fortunately, not every Republican office holder is a scaredy cat. Rock-ribbed conservative Sen. Tom Coburn of Oklahoma, who has just rejoined the Senate Gang of Six seeking a budget compromise, has spent much of this year trying to break Norquist’s hold on the Senate Republican caucus.

Norquist responded by claiming Coburn “lied his way” into office. The senator’s crime? Putting public policy — curtailing a foolhardy $6 billion tax subsidy for ethanol among other things — ahead of Norquist’s brand of ideological warfare.

Republicans looking to escape their straitjackets would do well to emulate Coburn. He has upheld the only pledges that any member of Congress should ever make: to his conscience, his constituents and the Constitution.

Margaret Carlson is a Bloomberg View columnist.