US:Shaken by the loss of her lead in Iowa, Hillary Clinton has made a dramatic tactical shift, a bandoning the lofty indifference of the frontrunner to move onto the offensive, attacking Barack Obama's character and honesty, as well as his policies.
On the Republican side, Mike Huckabee's surge into the lead in Iowa has prompted former Massachusetts governor Mitt Romney to make a long-anticipated speech addressing concerns about his Mormon faith.
With a new poll showing Mr Obama three points ahead in Iowa, Mrs Clinton has launched a series of attacks on him, accusing him of making dishonest claims about his healthcare policy and claiming that he broke election rules by channelling funds from his political action committee to elected officials in Iowa and New Hampshire.
"I have said for months that I would much rather be attacking Republicans, and attacking the problems of our country, because ultimately that's what I want to do as president. But I have been, for months, on the receiving end of rather consistent attacks.
"Well, now the fun part starts. We're into the last month, and we're going to start drawing a contrast, because I want every Iowan to have accurate information when they make their decisions," Mrs Clinton said in Iowa.
Mr Obama responded swiftly and his campaign has put up a website documenting Mrs Clinton's attacks on him.
"This presidential campaign isn't about attacking people for fun," Mr Obama said. "It's about solving people's problems, like ending this war and creating a universal healthcare system.
"Washington insiders might think throwing mud is fun, but the American people are looking for leadership that can unite this country around a common purpose, and that's what I'll continue to offer in this campaign."
Mrs Clinton has until recently avoided criticising her Democratic rivals directly, but her campaign is increasingly frustrated by what they see as a "free pass" Mr Obama is receiving from the media. The Clinton campaign is especially frustrated by the failure of the Obama "slush fund" story to resonate, arguing that the Illinois senator's questionable use of his lobbyist-funded Political Action Committee (PAC) shows up as hypocrisy his criticism of Mrs Clinton's decision to accept campaign contributions from lobbyists.
"Someone who runs on ethics and not taking money from certain people is found out to have at least skirted, if not violated, the FEC (Federal Election Commission) rules and used lobbyist and PAC money to do so," Mrs Clinton said.
She added that the difference between them was one of character. "It's beginning to look a lot like that," she said.
The rise of Mr Huckabee, a former Arkansas governor, has shaken up the Republican race and imperilled Mr Romney's strategy of winning early victories in Iowa and New Hampshire in the hope of gaining enough momentum to challenge Rudy Giuliani when more than 20 states vote on February 5th.
An ordained Baptist minister, Mr Huckabee has become the darling of many evangelical Christians who are suspicious of Mr Romney on account of his shifting positions on social issues and because, in some cases, they view Mormonism as a cult.
Some of Mr Romney's supporters have long urged him to make a speech on his faith along the lines of John F Kennedy's Houston speech in 1960, when he promised to be independent of the Catholic church.
The threat from Mr Huckabee appears to have persuaded Mr Romney to address the issue next Thursday in a speech on Faith in America at the George HW Bush presidential library in Texas.
"This speech is an opportunity for Governor Romney to share his views on religious liberty, the grand tradition religious tolerance has played in the progress of our nation, and how the governor's own faith would inform his presidency if he were elected. Governor Romney understands that faith is an important issue to many Americans, and he personally feels this moment is the right moment for him to share his views with the nation," Mr Romney's spokesman Kevin Madden said.
In his 1960 address to the Greater Houston Ministerial Association, Kennedy sought to lay to rest fears that, as the first Catholic president of the United States, he would take political direction from the Vatican.
"I am not the Catholic candidate for president. I am the Democratic Party's candidate for president who happens also to be a Catholic. I do not speak for my church on public matters - and the church does not speak for me," he said.
Mr Romney is not expected to go into details about the Mormon faith but will stress the values he shares with conservative Christians and speak about the American tradition of religious tolerance.
A third of voters who lean Republican describe themselves as "uncomfortable" with the idea of a Mormon president. That rises to 39 per cent of evangelical white Protestants, a core GOP group. Twenty-five per cent of evangelicals are "entirely" uncomfortable with a Mormon president.
