Tim Geithner, America's beleaguered Treasury secretary, faces a critical test of his credibility when he unveils a much awaited plan to take toxic assets off bank balance sheets – in an announcement that could come as soon as tomorrow.

Mr Geithner, whose initial announcement last month on the troubled asset purchase plan disappointed the market, has become the target of harsh criticism in Washington and on Wall Street with some questioning whether he can deliver.

Speaking on condition of anonymity, several senior Democratic figures questioned whether Mr Geithner would have the credibility with the markets and Capitol Hill to push through a new request for funds. “The more time passes the more convinced I am that Tim Geithner is becoming a liability for the administration,” said one lawmaker.