Barack Obama faced widespread condemnation today from both right and left for reneging on a promise on election campaign financing.

The Democratic presidential candidate, who normally gets a good press, found himself in the unusual position of being under attack not only from his Republican rival John McCain but papers such as the New York Times and Washington Post, think-tanks committed to election reform and even his own supporters.

Obama promised last year that, provided his Republican rival would too, he would abide by the election funding scheme set up after the 1974 Watergate scandal. The scheme provides each candidate with $85m (£42.5m) from the public purse to fight the election campaign from early in September to November 4, on condition they accept no outside money.

McCain, less successful at fund-raising than Obama, agreed yesterday to take public funding but Obama said he is not going to participate, the first presidential candidate ever to do so.

Obama's campaign team insisted the candidate made the decision because the existing system is open to abuse by the Republicans. But signing up for the $85m deal would be squander a huge advantage he has in fund-raising.

Up to the end of April, Obama raised $265m, spent mainly on his battle for the Democratic nomination with Hillary Clinton, compared with McCain's $115m by the end of May. Obama is on course to raise at least another $265m between now and the election.

Steve Schmidt, a senior adviser in the McCain campaign team, led the attack today, saying that breaking the promise raised questions about trust. "As we scrutinise Barack Obama's words, it is increasingly difficult for those of us with the responsibility of following this year's election closely to discern what Obama truly believes at his core on the issues of great importance to the American people," Schmidt said.

The Republican party today distributed copies of editorials from major US papers, including the New York Times and the Washington Post.

The New York Times, said; "The excitement underpinning senator Barack Obama 's campaign rests considerably on his evocative vows to depart from self-interested politics. Unfortunately, Mr Obama has come up short of that standard with this decision to reject public spending limitations and opt instead for unlimited private financing in the general election."

The Washington Post was also indignant: "Mr Obama had an opportunity here to demonstrate that he really is a different kind of politician, willing to put principles and the promises he has made above political calculations. He made a different choice ... "

Michael Malbin, director of the non-partisan Campaign Finance Institute, expressed disappointment and said the system likely would have worked well again this year. He thought the money provided by public funds should have been sufficient: "A million dollars a day doesn't look to me like chicken feed."

The Democratic senator Russ Feingold, an Obama supporter, called Obama's retreat "not a good decision".

Obama has said before he believes that the more money spent, the better the chance of winning an election. He today aired his first general election ad on television across 18 states, an early demonstration of his spending power.

In an article for USA Today, Obama wrote: "The decision not to participate in the public financing system wasn't an easy one - especially because I support a robust system of public financing of elections. But the public financing of presidential elections, as it exists today, is broken - and the Republican Party apparatus has mastered the art of gaming this broken system."

His team argues that while McCain has agreed to the limit, there are right-wing groups with millions at their disposal who could back campaigns such as the Swift Boat one in 2004 that challenged the Vietnam record of the Democratic candidate, John Kerry. His team also says that the Republican party is cash-rich compared to the Democrats. Both parties can spend on campaigning separate from their candidates.

Obama's decision could spell the end of publicly financed election campaigns.

In other developments, Obama announced today that he and Clinton are to campaign jointly next Friday, the first time since she conceded the race a fortnight ago.

Obama has said he would not make any public comment about his search for a vice-presidential running mate but a Democratic congresswoman, Carolyn Kilpatrick, disclosed today after meeting his team vetting candidates that John Edwards, who was the vice-presidential candidate in 2004, and the former senator Sam Nunn are both on the list.