Mitt Romney was born and raised in Michigan and has ties to Utah. Yet he chose to make his career, both in business and politics, in Massachusetts. Nearly every political problem Romney has today, at least those involving his policy positions, stems from that one decision.

Romney’s choice of home state affects his fortunes in ways big and small. Here in South Carolina, he was hurt by a widespread perception among conservative native Carolinians that Massachusetts is the font of all liberalism. “The voters link Massachusetts with gay marriage, easy abortion, traffic, pollution, the Kennedys, Dukakis, Kerry and Barney Frank,” says Clemson University political scientist David Woodard. “It’s anathema.” Even a Republican from the Bay State faces suspicion.

But Romney’s Massachusetts problem goes far deeper and extends far beyond South Carolina. To win election as a Republican in Massachusetts, and then to govern effectively, Romney had to align himself with the left side of the GOP. And to do that, he adopted positions that haunt him still.

Perhaps the most fateful was on abortion. Romney’s reputation as a “perfectly lubricated weather vane” — to use the memorable phrase of former rival Jon Huntsman — comes from his decision to run for Senate in 1994 and governor in 2002 as a strongly pro-choice candidate, and then to run for president in 2008 as a strongly pro-life candidate.

According to a new book by Boston journalist Ron Scott, when Romney was planning that ’94 Senate run, he commissioned polling that showed a pro-life candidate could not win statewide election in Massachusetts. So Romney, who said he was personally pro-life, became politically pro-choice.

And not just pro-choice, but ardently pro-choice. “I am not going to change our pro-choice laws in Massachusetts in any way,” Romney said in an Oct. 29, 2002, debate. “I will preserve them. I will protect them. I will enforce them. I do not take the position of a pro-life candidate. I am in favor of preserving and protecting a woman’s right to choose.” When The Boston Globe said there was not a “paper’s width” of difference between Romney and his Democratic opponent on abortion, Romney proudly quoted the paper.

If Romney had chosen a less liberal state to live in, he would not have had to do that — and, of course, he would not have had to switch back to a pro-life position in 2004-2005, as he formed a political action committee and began working toward a run for the Republican nomination for president.

As a candidate for office in Massachusetts, Romney also had to take positions on guns, global warming and gay rights that later caused him difficulties in Republican presidential politics. He even had to renounce Ronald Reagan — an extremely unwise thing to do in today’s GOP. “Look, I was an independent during the time of Reagan-Bush,” Romney said in a 1994 debate with Sen. Ted Kennedy. “I’m not trying to return to Reagan-Bush.” Now, of course, Romney sings Reagan’s praises at nearly every campaign stop. If he hadn’t run in Massachusetts, he wouldn’t have had to bash Reagan in the first place.

But, after abortion, the most devastating consequence of Romney’s choosing Massachusetts has been the issue of universal health care. In extending coverage to everyone in the state, Romney helped fulfill a long-time liberal goal; just look at the love-fest with Kennedy at the bill’s 2006 signing ceremony. But Romney did not effectively control rapidly rising health care costs. And he could not have anticipated how deeply unpopular universal coverage schemes would become with the Republican base after Obamacare.

In the campaign, Romney has blamed the Democratic Massachusetts legislature for Romneycare’s problems and denied vigorously that he believes his bill would be a good model for the nation. It’s a difficult position to take on his signature achievement in office. And it would not have happened had Romney not chosen to run in Massachusetts.

Given all that, it’s no wonder Romney is running for president more as a former businessman than as a former governor. On the stump, he spends far more time discussing his business career and job-creation record than he does his time as governor. Indeed, at an election-eve rally in North Charleston, S.C., Romney discussed details of how he helped start the office-supply firm Staples but never once mentioned that he had been a governor.

It all stems from that single decision, many years ago, to live in Massachusetts rather than Michigan, or Utah, or some other less liberal state. Now, it’s part of who Romney is, and it can’t be undone.