Obama hits back at Hillary

Chicago - Barack Obama, fresh from losses in Ohio and Texas, on Wednesday promised a more aggressive approach in his battle with Hillary Clinton for the Democratic US presidential nomination.

The Illinois senator vented frustration at what he called a "very negative" campaign his rival had run against him in recent days and said it seemed to be a factor in his setback.

The attacks "had some impact," Obama told reporters as he headed back to his home city of Chicago from Texas, a state that along with Ohio and Rhode Island went to the former first lady and New York senator, breaking his month-long winning streak and breathing new life into Clinton's campaign.

Voters blame trade deals

Clinton labeled Obama, a first-term senator, too inexperienced to lead US foreign policy. She pressed that charge with an ad juxtaposing sleeping children, the sound of a ringing White House phone and an ominous warning that if a world crisis were to erupt, Americans need a "tested" leader.

Clinton also criticised what she called Obama's inconsistencies on hemispheric trade, an issue important in Ohio, where many voters blame trade deals for job losses.

Instead of only his usual message that he is better equipped to lead on foreign policy because he showed better judgment than Clinton by opposing the Iraq war early on, the Illinois senator bluntly derided Clinton's assertion that her eight years as first lady counted as foreign policy seasoning.

'Think it's important to examine the argument'

"I hope people start asking, what exactly is this foreign experience that she's claiming? I know she talks about visiting 80 countries. However it's not clear...was she negotiating treaties or agreements, or was she handling crises during this period of time?" Obama asked.

As the Clinton campaign has urged reporters to more closely examine Obama's ties to a Chicago developer, Tony Rezko, facing federal corruption charges, Obama suggested Clinton's record on ethics should be fair game, too.

"She's made the argument that she's thoroughly vetted in contrast to me," Obama said. "I think it's important to examine that argument because, if the suggestion is somehow that on issues of ethics or disclosure or transparency, that somehow she's going to have a better record than I have, and will be better able to withstand Republican attacks, I think that's an issue that should be tested."

Obama also expressed pique at her argument that some of her wins in big states like California and Ohio were more significant than his sweep of many small states like Idaho and Nebraska.

Did not flinch from the role

Some political strategists warn that going negative can backfire, especially in primary contests when the rivals are from the same party.

And a central message of Obama's candidacy is his pledge to rise above the divisive politics of the past.

Clinton, who poured her energy over the last few weeks into salvaging her candidacy, did not seem to flinch from the role of aggressor, as she told Ohio voters she was a "fighter" and "doer" ready to take on big corporations and other interests blamed by some working class voters for their economic struggles.

- Reuters