What’s the biggest difference between the victorious 2013 House special-election campaign of Mark Sanford and the losing 2013 Senate special-election campaign of Gabriel Gomez? Simply, a willingness to take on Obamacare.

Despite the kind of résumé that’s a political consultant’s dream — assimilated immigrant who still speaks his native tongue, aircraft-carrier-landing naval aviator, Navy SEAL and an MBA from the Harvard Business School to go along with his camera-friendly wife and four children — Gomez came up short in his special-election campaign against Democratic Rep. Edward J. Markey, who was first elected to Congress before Tom Brady was born and had never before run statewide. Lackluster fairly describes it: It was the lowest turnout in history for a Massachusetts Senate race, and Gomez pulled in about 525,000 votes — about half of the number who voted for Scott P. Brown in January 2010 when the race became a referendum on Obamacare, the main issue that would propel Republicans to a House majority later that fall.

Regrettably, Gomez, who used some of Romney’s consultants and playbook, followed the failed model of 2012 instead of embracing what worked in 2010 and works still. He could have won with a different campaign conversation, emulating Sanford’s successful congressional bid last month, wherein Sanford distinguished himself from his opponent, and made Obamacare a central focus of the campaign.

Markey certainly gave Gomez the opening: In a debate earlier this year, Markey referred to his vote for Obamacare in March 2010 as “the proudest vote of my career.” And in a recent blog post on The Huffington Post, Markey called Obamacare “the most important bill I’ve ever voted for.”

Yet Gomez failed to make use of Markey’s cheerleading for Obamacare in either his paid or earned media. In none of the TV ads Gomez or apparently any outside group aired does the word “Obamacare” cross the announcer’s lips, and in a 10-minute interview Gomez did just two days ago on Fox News Sunday — his last friendly national interview before the electorate headed to the polls — he failed to mention the unpopular program at all.

In late May, Independent Women’s Voice reached out to the Gomez campaign to ask him to sign the Obamacare Repeal Pledge; we believed the issue could make the difference in the success or failure of his race. Gomez’s camp responded that he was not signing any pledges.

Making matters worse, in a GOP debate during the primary campaign, he declared, “I think the overall theme of Obamacare was right.” Further, his campaign website “Issues” page failed to include an explicit promise to work to repeal this behemoth and even spoke approvingly of Massachusetts’ own universal health care program — signed into law by Mitt Romney — which, predictably, has been shown to raise prices and decrease quality and choice.

As a consequence, Massachusetts voters were left with no clear distinction between the two candidates on a fundamental issue. Anti-Obamacare Democrats and independents — and every national poll shows there are tons of them — were given no reason to vote for Gomez, as many had for Brown in 2010 when he ran as the 41st vote against Obamacare. (In contrast to his 2012 campaign, which he then lost. Pattern anyone?)

A valuable counterpoint here is the experience of Sanford, whose extramarital affair and ensuing scandal caused him to leave office in early 2011 with dismal approval ratings and who at one point was running so far behind his Democrat opponent in his May special House election that he was written off for dead.

Yet rather than blur the issues distinction between himself and his opponent, Sanford reinforced it. He signed the IWV Obamacare Repeal Pledge and regularly drew contrasts between himself and his opponent on the issue in both his paid and earned media.

The fact that he had signed the Repeal Pledge allowed IWV to raise the funds necessary to launch a $250,000 education campaign, ensuring that likely voters in his congressional district understood just how liberal his opponent was.

A survey conducted for IWV in the immediate aftermath of that race revealed that the single biggest reason given by voters who voted for Sanford was that he had signed the Repeal Pledge, while his opponent, the sister of well-known TV personality Stephen Colbert, had refused to.

In any number of campaigns over the past two cycles — beginning in the January 2010 Senate special election in Massachusetts and continuing through a series of 2012 Senate races, and into the 2013 special House election in South Carolina — signing the IWV Repeal Pledge has been seen by voters not just as an indicator of a candidate’s seriousness about overturning Obamacare but as a larger marker about their opposition to government overreach and excessive intrusion. There’s simply no reason any candidate who opposes Obamacare should not sign it.

A mid-May poll for CNN/ORC shows that, 54 percent to 43 percent, a majority of adults nationwide oppose Obamacare. An April survey for the Kaiser Family Foundation Health Tracking Poll shows that a majority of adults nationwide, 53 percent to 33 percent, believe those opposed to Obamacare should “continue trying to change or stop it, so it has less impact on taxpayers, employers and health care providers.”

Obviously we’ll never know for sure whether, had Gomez signed the Repeal Pledge and made Obamacare a central point of differentiation between himself and his opponent, he would have won Tuesday’s contest. But we’re willing to bet he’d have at least run a lot closer to Markey than he did. And we’re willing to bet that if he fails to sign the Repeal Pledge and fails to make Obamacare — which by then will be headlong into complex, confusing, costly implementation — a major issue against Markey next year, he’ll end up losing again.

Heather R. Higgins is president and CEO of Independent Women’s Voice. Kellyanne Conway is president and CEO of the Polling Company Inc. and WomanTrend and a board member of Independent Women’s Forum.