Harsh words flew on Friday between the rival Democratic campaigns of presidential hopefuls Barack Obama and Hillary Clinton after Obama gained the backing of the country's only Hispanic governor.
Rival Hillary Clinton's campaign dismissed the nod from New Mexico Governor Bill Richardson as coming too late to have any effect, while Obama's staff hit out at Clinton's alleged dishonesty after records detailing her years as first lady were made public.
The fresh mudslinging capped off a week in which the hard-fought race took on an increasingly nasty tone with both sides trading charges of misleading the public and trying to divert attention from political scandals.
On the campaign trail, Richardson's move was a setback for Clinton and gave Obama a supporter with influence among pivotal Hispanic voters -- who have leaned towards his rival -- and well-known ties to the Clinton family.
The New Mexico governor called Obama a "once-in-a-lifetime leader" who could inspire voters, repair America's image abroad and overcome racial and political divisions.
Richardson served as energy secretary and UN ambassador in the administration of president Bill Clinton and carried out delicate diplomatic missions in North Korea and Saddam Hussein's Iraq.
He dropped out of the race for the Democratic nomination on January 10 after a poor showing in the early state-by-state primary and caucus contests.
The Clinton campaign played down the significance of the endorsement, with chief strategist Mark Penn saying "the time when he could have been most effective has long since passed."
The Obama campaign this week pounced on the release this week of White House records during Clinton's tenure as first lady, saying the documents exposed a lack of candor about her role in policy decisions and were "just the latest in what has become a legacy of misleading voters."
The Illinois senator's campaign issued a statement Friday saying: "Honesty is a crucial metric in this race because the Democratic nominee is going to be running against John McCain, who is viewed by voters as one of the most trustworthy politicians in America."
For weeks, Obama and Clinton, his Senate colleague from New York, have been locked in a battle for the right to face McCain in the November 4 presidential election.
Richardson praised Obama's widely-publicised address on race and politics Tuesday, in which he tried to blunt the furor over comments by his former pastor Jeremiah Wright, saying the senator's words were "courageous."
Clinton's aides meanwhile accused Obama trying to shift attention from his troubles, without openly mentioning the row over his controversial pastor, whose fiery sermons have been televised repeatedly in recent days.
"At this point, it is no secret that the Obama campaign is in political hot water, given the news stories of the last several weeks, and is basically desperate to change the subject," Phil Singer, deputy communications director for the Clinton camp, told reporters.
After a Gallup poll earlier in the week indicated that Obama had taken a hit due to the pastor-affair, a CBS poll on Friday suggested that most Americans felt he did a good job explaining his views on race in America in a landmark speech on Tuesday.
Meanwhile, the State Department apologized over revelations that employees opened passport files for all three main contenders for the White House without authorisation.
State Department spokesman Sean McCormack confirmed the passport records for Obama, Clinton and Republican candidate John McCain were all examined without approval and promised a full investigation.
Secretary of State Condoleezza Rice had by Friday afternoon telephoned all three candidates to apologise for the incidents, which the State Department attributed to "imprudent curiosity."
Estimates show Obama leading the former first lady in nominating delegates 1,628 to 1,493. But Clinton, who also trails in the popular vote, hopes to build a case for her candidacy with a triumph in the April 22 primary in delegate-rich Pennsylvania, where she has a big lead in opinion polls.
Neither candidate has won the 2,025 delegates needed to secure the nomination and the fight could go to the floor of the party convention this August in Denver, Colorado. (AFP)
Barbs fly in contentious US White House race