John Kerry opened a crucial week in his bid for the White House yesterday with a broadside against George Bush on one of the most emotive issues of the campaign, saying the President had jettisoned science for "extreme right-wing ideology" by curbing federal funding on stem cell research.

John Kerry opened a crucial week in his bid for the White House yesterday with a broadside against George Bush on one of the most emotive issues of the campaign, saying the President had jettisoned science for "extreme right-wing ideology" by curbing federal funding on stem cell research.

Shifting focus from international to domestic issues, Mr Kerry delivered his attack in a speech in New Hampshire, a state narrowly carried by Mr Bush four years ago, but which the Democrats have hopes of winning on 2 November. Alongside him was the actor Michael J Fox, who suffers from Parkinson's disease, one of the diseases for which a cure could be hastened by stem cell technology.

The Democratic candidate, who promises annual spending of $100m on stem cell research, said that with his ban on funding for new cell lines, Mr Bush had "tied the hands of our scientists" and "made the wrong choice to sacrifice science for extreme right-wing ideology."

Mr Kerry went on to list a series of other areas, ranging from water and air quality to global warming and high-tech jobs, where, he claimed, the Bush administration had ignored science and evident fact for purely political ends.

Mr Bush was in Iowa yesterday, a state he lost to Al Gore in 2000. At a stop in Des Moines, he signed into law the fourth round of tax cuts of his Presidency - re-inforcing his campaign message that money should be spent by those who earn it, rather than by government. "Families will spend this money much more wisely than we can," Mr Bush declared.

The Working Families 2004 Tax Relief Law signed by Mr Bush extends some of the tax cuts passed earlier in his Presidency. The $145bn measure will affect over 90 million Americans by extending child tax credits and slightly reducing taxes for married couples.

The competing claims came at the start of a week that sees two candidates' debates: one between the Vice-President, Dick Cheney, and his would-be successor, Senator John Edwards, in Cleveland tonight; the second between the Presidential candidates at a "town-hall meeting" on Friday at Washington University in St Louis.

They come amid polls showing that Mr Kerry is now level with Mr Bush after his strong performance in the first debate on foreign policy in Miami on Thursday last week. Mr Kerry's supporters believe that their man can regain the initiative, as the debate topic shifts to domestic issues such as the economy and health care, which usually favour Democrats.

The tightening contest has given extra importance to an already intriguing match-up between the youthful Mr Edwards and the dour Mr Cheney, probably the most powerful Vice-President in recent US history.

Normally the Vice-Presidential debate would make few sparks fly. Four years ago Mr Cheney and his then Democratic opponent, Joe Lieberman, were criticised for being "too nice" to each other. This time, however, the atmosphere could be far less gentlemanly.

Mr Edwards will try to brand Mr Cheney the misguided architect of the Iraq war, with his claims about Saddam Hussein's non-existent weapons of mass destruction and the unproven links between Saddam and al-Qa'ida.

Mr Edwards received more ammunition this weekend with an article in The New York Times that raised new doubts about the aluminium tubes imported by Saddam. Mr Cheney used the tubes as evidence that the Iraqi dictator was "reconstituting" nuclear weapons but, since the war, it has become clear that Iraq's nuclear programme had been abandoned.

Mr Edwards will also use the shortcomings of reconstruction in Iraq to highlight Mr Cheney's five-year stint as the chairman of Halliburton, the oil services company which has allegedly been favoured in the awarding of business contracts in Iraq. For Democrats the very name Halliburton is shorthand for the corporate greed and cronyism they say is the hallmark of the Bush administration.

For his part, the Vice-President will try to portray his opponent as too inexperienced to be allowed near the levers of foreign and security policy. But Mr Cheney cannot afford to be too gruff and imperious. If he is, "the Republican ticket will risk looking like a couple of grumpy, ill-tempered old men", said one political analyst, referring to Mr Bush's debate performance last week, when he came across as peevish, impatient and incapable of listening to an opposing point of view.

Mr Kerry received a separate boost yesterday with a statement of support from 180 former US ambassadors. The envoys issued a letter stating it was "imperative" for US national security that Mr Bush be defeated. The President had "needlessly squandered the good will and support of the world following the 11 September attacks," the letter said.