“Michelle, my belle, these are words that go together well,” sang Paul McCartney. Perhaps Mitt Romney should feature this Beatles’ hit at his campaign rallies.

Why? Without Rep. Michele Bachmann (R-Minn.) clearing the field for him, the former Massachusetts governor might be facing the same fate as another candidate once anointed as the GOP frontrunner despite very weak internal polling numbers. The name of that candidate: George Romney, then governor of Michigan.

The media labeled the elder Romney as the electable GOP moderate in a party controlled by a new conservative movement. By the 1968 New Hampshire primary, father George dropped out due to lack of conservative support.

Forty-three years later, his front-running son finished behind the pizza man in the Ames straw poll. Admittedly, the younger Romney made no effort to get votes in Ames, and polls in New Hampshire show him winning the first-in-the-nation primary. But the lack of grass-roots Iowa enthusiasm cannot be dismissed.

Romney’s campaign doesn’t seem worried. Here’s the likely reason:

His main rivals have been disappearing from the field ever since Bachmann made her presidential ambitions known. Most political observers thought Sarah Palin would crush Bachmann if former Arkansas Gov. Mike Huckabee didn’t do it first. No one considered Bachmann to be more than a sideshow.

First out of the ring was Huckabee, whose star rose after the 2008 Ames straw poll. He once loomed as Romney’s main threat. His former supporters backed Bachmann this time. Did Huckabee not run because he suspected Iowa might not be as favorable as the pundits were predicting? 

If you doubt it, consider the relative ease by which Bachmann has kicked Palin, another darling of the right, to the political curb. The 2008 GOP vice presidential nominee seemed the biggest beneficiary of the Huckabee exit. It made Iowa loom even larger in the presidential jockeying, with the Hawkeye State one of her best venues.

But Palin knows she and Bachmann are locked in a zero-sum game. As Bachmann’s constituency grows, Palin’s star dims.

That Palin still thinks about running for president is evidenced by her appearance at the Iowa State Fair right before the voting. If you believe her story about it being merely a coincidence of timing, then we needn’t ask your opinion as to why Texas Gov. Rick Perry chose to announce for president on the morning of the vote. He hoped to siphon off enough votes from Bachmann to let another candidate sneak into first place. Palin and Perry thought their maneuvering might enable former Minnesota Gov. Tim Pawlenty to win.

Tim who? Remember, he was once seen as a likely competitor to Romney, able to compete for the “moderate” constituency.

A viable T-Paw candidacy would have made the primary math better for a Tea Party conservative. But Pawlenty’s attacks on Bachmann backfired. He championed his record at making the government work in Minnesota while belittling Bachmann’s efforts at standing up to politicians in Washington. Like Huckabee and Palin before him, he became the latest former governor to underestimate the political savvy of the Congresswoman.

By vanquishing Pawlenty, Bachmann has given Romney hope of solidifying support from the McCain constituency he lost in 2008. Moderate by GOP standards, these voters still can be the core of a winning primary constituency under the right circumstances. Bachmann, therefore, has been, and will continue to be, the key to Romney’s potential success.

There are now three likely scenarios in the GOP, assuming no other major entries. The worst-case scenario for Romney is that Perry wins the intraparty battle against Bachmann for the conservative right, leaving a Romney-Perry shoot-out.

The other scenarios are more favorable: a three-way fight splitting the conservative wing; or, Bachmann sends Perry back to the Alamo and has her own shoot-out with Romney.

Romney is a businessman, so he knows the bottom line. That is, the prevailing view of him as the strong favorite misreads the GOP terrain. Many leading pundits have said the real race starts only when the alternative to Romney emerges.

But Romney’s best hope is that the surging Bachmann can either stop Perry or leave both of them sufficiently wounded to let the former Bay State governor win ugly.

To get down to Romney, right now it looks like it is all up to Michele.

Paul Goldman is the former chairman of the Democratic Party of Virginia. Mark J. Rozell is professor of public policy at George Mason University.