John McCain accused Barack Obama of being a liberal, high-taxing threat to Middle America yesterday after being confronted with strong evidence that his Democratic opponent has wiped out his postconvention bounce and regained the initiative.

After a week of economic turmoil and his damaging remark on Monday that “the fundamentals of our economy are strong” – spoken as Lehman Brothers was declaring bankruptcy – Mr McCain aggressively sought to regain his footing.

A string of new polls, however, showed Mr Obama back in the same position as he was before the party conventions: enjoying a small lead over his Republican opponent.

The surveys also suggested that the impact of Sarah Palin, while still energising the Republican Party, could be proving more short-lived, with Mr Obama regaining his advantage among female voters in two new national polls. Yet with 46 days to go before the election, the race remains extremely close and unpredictable. Bill Clinton said that Democrats had to work hard because the race will be “competitive until the end”.

In a new twist, the FBI and Secret Service were investigating a breach of Mrs Palin’s private e-mail account by computer hackers, who appeared to have proved that the Republican vice-presidential nominee and Alaska Governor had used her private Yahoo! e-mail account to conduct official state business – a potential breach of Alaskan law.

The hacking controversy comes as Mrs Palin’s personal e-mail accounts were coming under closer scrutiny as part of an Alaskan ethics investigation into whether she abused her office to settle a personal score. She is alleged to have fired her police chief because he refused to dismiss her brother-in-law, a state trooper who had gone through an ugly divorce with her sister.

Her husband, Todd, who has been subpoenaed, was due to give evidence today but it was unclear last night if he would comply.

Mr McCain’s new advertisement, to be aired nationally, seeks to link Mr Obama to the “liberal” Democratic-controlled Congress, which has even lower approval ratings than President Bush. The narrator says: “We would pay: painful income taxes, skyrocketing taxes on life savings, electricity and home heating oil.” Then, to a picture of a sleeping baby, it ends: “Can your family afford that?”

In a combative appearance in Iowa, Mr McCain sought to tie Mr Obama to the leadership of the mortgage companies Fannie Mae and Freddie Mac, which were bailed out by the Government this month. The former head of Fannie Mae was Jim Johnson, who quit as part of Mr Obama’s vice-presidential vetting team after it emerged that he had received favour-able rates on his mortgage. “Whose side do you think he is on?” Mr McCain asked of Mr Obama.

Later in the day, at a rally in New Mexico, Mr Obama responded by criticising Mr McCain’s proposal earlier this week that there should be a formal investigation into what caused the chaos on Wall Street. The Democrat also referred to his rival’s call for tighter regulation of the the financial markets, a position Mr McCain has long opposed.

“We do not have time for commissions, and we can’t afford to lurch back and forth when dealing with an economic crisis,” Mr Obama said.

Seeking to get ahead of the financial tidal wave swamping Wall Street, Mr McCain is due to give a big speech today outlining how he would solve the crisis.

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