Obama has changed his position so many times in order to pander to everyone, even conservatives, to the point where he has last any credibility he had. 

Obama Playing Voters for Dupes

A signature moment of Barack Obama's primary campaign came last November in Des Moines, Iowa. He gave a speech at the Jefferson-Jackson Dinner that electrified the crowd and gave his campaign a kick that helped win the Iowa caucuses -- a victory without which he wouldn't be the Democratic nominee.

Obama declared that "the same old Washington textbook campaigns just won't do." Deploring "triangulating and poll-driven positions," he said that "telling the American people what we think they want to hear instead of telling the American people what they need to hear just won't do." The Democratic Party had been at its best, he told the crowd, when "we led, not by polls, but by principles; not by calculation, but by conviction."

"I run for the presidency of the United States of America because that's the party America needs us to be right now," he vowed, staking his candidacy on the achingly idealistic premises of a new, more forthright and uncalculating politics.

What makes Obama's "textbook" dash to the center so extraordinary is not just its speed, but how it falsifies the very essence of his candidacy. It's as if Bill Clinton won the Democratic nomination in 1992 and announced suddenly that actually he was not a "new kind of Democrat"; or if George W. Bush, after winning his party's nomination in 2000, forswore "compassionate conservatism"; or if John McCain, after winning the GOP nomination this year, declared in favor of a hard deadline for withdrawal from Iraq.

In the past few weeks, Obama has broken two pledges (to take public financing in the general election and to filibuster legal immunity for telecoms that cooperated with the government in terrorist surveillance); has belittled his own rhetoric during the primary campaign (saying it could get "overheated and amplified" on the issue of trade); redefined his promise to meet without preconditions with the leaders of hostile states until it's basically meaningless; endorsed a Supreme Court decision striking down a Washington, D.C., gun ban his campaign had previously said he supported; and made muddy, centrist-sounding statements about his positions on Iraq and abortion that he had to go back and try to clarify.

Has there ever in recent political memory been so much calculation and bad faith by a politician who has made so much of eschewing both? We now know that Barack Obama is not naive, but his ardent supporters are. Obama exhorted them to "believe" -- one of his favorite words -- in him and his virtue above all, and as soon as they gave him the nomination he wanted, he showed how foolishly credulous they had been. When it comes to triangulating, he's Hillary Clinton without the baggage.

RCP Article