A decade ago, political scientists Lawrence Jacobs and Robert Shapiro wrote an excellent book called Politicians Don't Pander, in which they argued convincingly that the popular image of politicians slavishly following public opinion to determine where they should change their positions was bunk. That, however, was before Mitt Romney emerged on the scene. Yes, Mitt has a pandering problem, but if you're a Republican, it's really two problems.
The first is that Mitt's reputation for pandering is so firmly entrenched that it would make it easy for the Obama campaign to paint him as, well, an untrustworthy panderer who'll say anything to get elected. And since this has been widely viewed as Romney's principle character flaw for some time, it will be the topic of extensive press discussion during a general election. He won't be able to escape it.
The second problem for Republicans is that if Romney wins, he might not be reliably conservative in his policies. The reason is that once he becomes president, his audience will change. So far, Romney's political career can be divided into the Massachusetts phase, in which he was a pro-choice, health care reforming moderate, and the national phase, in which he's been a right-wing conservative. There are variations within the second phase, but for the last four years he's had only one audience in mind: Republican primary voters. Were he president, his audience would be more liberal than his current one, but not as liberal as the one he faced in Massachusetts. That's where it gets complicated.
As president, Mitt would fear retribution from multiple directions. If conservatives mounted a primary challenge to him in 2016, it would be very bad news (in recent decades, presidents who get primary challenges almost inevitably lose, though cause and effect are difficult to untangle). So he'd have to keep the right happy. On the other hand, if he wanted to maintain the support of the broader electorate, he couldn't be catering to the right's every whim the way he has at times. It would be a difficult needle to thread.
Add in the fact that as someone already distrusted by the right, Romney would be more likely than a different Republican to get a primary challenge in 2016 (they won't be inclined to cut him much slack), plus the fact that the narrative of radical Tea Partiers hell-bent on destroying the country to serve their ideological ends is now a familiar one, and it gets even worse. The Romney presidency would be consumed with debates about who he's pandering to, and whether it's going to work. If it had a motto, it would be, "President Romney: Please Don't Hate Me."
So if you're a Republican primary voter, there are multiple reasons to feel uneasy about Romney being your nominee. He may be able to overcome that unease. But it won't be easy.