Bachmann's candidacy was immediately eclipsed by Rick Perry's announcement that he was running. But in four debates since then, Perry has failed to live up to Republican voters' platonic ideal of a governor of Texas -- and gave Romney a high-visibility opponent he could dominate in head-to-head repartee.
In the meantime, the threat of a Chris Christie candidacy, which threatened to eat into Romney's support, turned into a boon when Christie reiterated his non-candidacy one week and endorsed Romney the next. Good luck on good luck.
Now Herman Cain has zoomed past Romney in some polls. As a conservative without political experience he has credentials that would appear to trump Romney's in a party whose ranks of activists have been swelled by tea partiers determined to cut back government.
But his 9-9-9 plan is under attack from other candidates, and although Cain resembles Romney in some respects -- business success, failed bids for the Senate -- Romney has far more in the way of serious policy advisers and proposals. He speaks with more assurance and has been able to drill down in detail, while Cain tends to repeat talking points.
Romney's luck may run out at some point. He's topped 25 percent in only three of 80 national polls taken this year, suggesting vulnerability in a one-on-one contest. On some issues and on basic stance, he is out of line with the median Republican voter.
But luck tends to come from those who are well prepared. Romney has learned from his mistakes in 2008, and he is effectively executing a strategy that seems in line with his experience and recorded positions. Perhaps more important, he's shown a sense of command that none of his rivals has matched. Lucky -- and something more.