A team of aides to John McCain are monitoring closely a potentially damaging Alaskan ethics investigation into Sarah Palin, after her husband and top staff were summoned to give evidence.

The Republican’s presidential campaign is preparing an aggressive push back against the inquiry if Mrs Palin is found to have abused her office to settle a personal score – the central allegation in the case. The final report from the investigation has been expedited to October 10, three weeks before the election.

The investigation is one of the few dark clouds hanging over Mrs Palin since being named as the running-mate of Mr McCain two weeks ago. Aides to Mr McCain are unsure what the outcome will be and whether “Troopergate” could derail the campaign.

A bipartisan panel from the Alaskan state legislature, headed by a Democrat, has been investigating after allegations in July that Mrs Palin pressured the police chief to dismiss a state trooper involved in a divorce from her sister.

The police chief, Walter Monegan, claimed that Mrs Palin fired him when he refused to dismiss the trooper, Mike Wooten. The Alaskan governor said that she removed Mr Monegan because of a dispute over budget issues.

Mrs Palin initially denied that she or any of her staff had contacted Mr Monegan about Mr Wooten, who admitted attacking his stepson, 10, with a taser gun, and whom Mrs Palin accused of threatening her father. Yet last month she released a tape-recording of a senior aide pressuring Mr Monegan to dismiss Mr Wooten, and conceded that members of her staff had made about two dozen contacts with state officials about him.

“I do now have to tell Alaskans that such pressure could have been perceived to exist, although I have only now become aware of it,” Mrs Palin said at a press conference on August 13.

Mr Monegan claimed in the past fortnight that Mrs Palin contacted him personally about Mr Wooten.

On Friday the Alaska Senate Judiciary Committee voted to issue subpoenas to Todd Palin, the husband of the Republican vice-presidential nominee, and a dozen members of her gubernatorial team, including her chief of staff and deputy chief of staff.

Steve Branchflower, a retired state prosecutor hired to conduct the inquiry, said that he had taken the rare step of requesting the subpoenas because most of the state employees had either refused to submit to his questioning or had initially agreed, then cancelled their appointments. He said that Mrs Palin would not be summoned. She said that she would cooperate fully with the investigation and denied any wrongdoing.

Mr Branchflower said that he wanted to subpoena Mr Palin because he was the “principal critic” of Mr Wooten’s continued employment. In January 2007, just after Mrs Palin was sworn in as governor, Mr Palin met Mr Monegan to show him a file on Mr Wooten put together by a private investigator hired by the family.

The move came as Mrs Palin’s record as mayor of the Alaskan town of Wasilla, and then as governor, received detailed scrutiny in The New York Times and The Washington Post yesterday. After what appeared to be thorough research involving inquiries, interviews and document searches by both newspapers, neither found any significantly damaging evidence against Mrs Palin. They painted a picture, however, of a fiercely competitive woman who had awarded political jobs to friends and donors and was accused by some in Alaska of using her office to carry out personal vendettas.

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