A new word entered Sen. Barack Obama’s (D-Ill.) political vernacular last week. He no longer simply changes his positions when politically convenient or advantageous. No, the oratorical whiz of the 2008 election is now “refining” his policies.

[IMGCAP(1)]Thanks to the guy who told us “words matter,” issue “refining” as political speak now enters the realm of such classics as “revenue enhancement” (tax increases) and “strategic redeployment” (retreat). If this were just another politician, this kind of behavior would hardly be surprising.

But for the past 18 months, Obama has marketed himself to his supporters, especially his youngest backers, as a new kind of candidate, wrapping himself in “change we can believe in.”

But can we? I’m not knocking Obama simply because he had a change of heart or mind on a particular issue. It’s important that as candidates debate policy, voters give them the flexibility to rethink positions when circumstances change.

Finding one’s way through what is a political thicket of policy positions isn’t easy for any candidate. Voters want leaders with consistency and principle, but they also want men and women who constantly assess the social, economic and security environment as it is and as it might be.

When it comes to crafting policy, consistency is a good thing and at times essential; so is a willingness to revisit a position when circumstances dictate.

If the state of the economy worsens or a serious national security threat arises, it would be irresponsible for politicians not to acknowledge those changes and adjust their policies accordingly. After Pearl Harbor, what had been an isolationist Congress abruptly changed course because circumstances had changed, in that instance dramatically.

After 9/11, President Bush, who had opposed nation building in the 2000 campaign, reversed himself and embraced it as part of his Iraq policy. Whether one agrees or disagrees with that decision, it was a radically changed national security environment that led Bush to a proactive stance on the war on terror.

But is it changed circumstances or political expediency that is driving Obama’s policy U-turns? If Sen. Obama has now learned that the surge in Iraq has worked, that FISA is, in fact, necessary to protect the security of the United States, that overly restrictive gun laws don’t reduce crime, or that free trade does more good than harm, so be it.

If he now sees that welfare reform of the mid-1990s was necessary, that not all late-term abortions can be justified or that Iran “does pose a serious threat” to the United States after all, then his reversals on all these positions could be justified.

But that isn’t what he has been saying. To the contrary, he is trying to convince the American people that his recent policy switches on all these issues were, in fact, his views all along. That he is simply “refining” those original positions, not reversing them.

In the case of his wholesale abandonment of public financing, his explanation simply defies credulity. When faced with his first test of choosing principle or political advantage, Obama failed to live up to his own standards. That left some of even his staunchest supporters with a queasy feeling, wondering what happed to the high-minded principles that drew them to him in the first place.

Critics have tried to equate Sen. John McCain’s (R-Ariz.) change on domestic oil drilling with Obama’s policy switches. But in McCain’s case, economic and social circumstances did change significantly.

When gas goes to more than $4 a gallon, candidates ought to rethink every energy option — more domestic drilling, more nuclear power, more conservation and more alternative power sources. In adopting a comprehensive approach, McCain did exactly that.

Last week on Hannity & Colmes, National Review Editor Rich Lowry asked Democratic pundit Michael Brown a very compelling question. How would he explain Obama’s recent major policy switches to one of the millions of young, naive Obama supporters so personally invested in their candidate’s promise of “change you can believe in?”

Brown, without a moment’s hesitation, proffered that in order to get elected, all presidential candidates change positions once the primaries are over. Everybody moves to the center.

His advice to young Obamaniacs could be summed up as, “Winning isn’t everything. It’s the only thing.”

That may work for most politicians, but it’s problematic for one who has set himself apart as a different kind of candidate, one who rejects the old politics. He may discover there is a high a price to pay when one walks away from the central promise and premise of a political campaign. Just ask George H.W. Bush, who once pledged, “No new taxes.”

Barack Obama has not rejected his original positions as wrong, misguided or even out of date. Instead, he has pushed principle aside and now offers his young idealists and the rest of the American people a general election theme — “refinement you can believe in.”

David Winston is president of The Winston Group, a Republican polling firm.