In the U.S. presidential election campaign, Hillary Clinton is stepping up her criticism of rival Democrat Barack Obama one week before critical primary votes in Texas and Ohio. VOA National correspondent Jim Malone has more.

Senator Clinton highlighted her experience in foreign policy during a speech in Washington, and seemed to compare rival Barack Obama to President Bush when he won the presidency with relatively little foreign policy experience in 2000.

"We have seen the tragic result of having a president who had neither the experience nor the wisdom to manage our foreign policy and safeguard our national security. We cannot let that happen again," she said. "America has already taken that chance one time too many."

Clinton has become more aggressive in recent days in attacking Obama for what she says are false charges in some of his campaign literature that question her stands on trade deals and health care reform.

"Shame on you, Barack Obama. It is time you ran a campaign consistent with your messages in public. That is what I expect from you," she said. "Meet me in Ohio and let us have a debate about your tactics and your behavior in this campaign."

Obama told reporters that he was surprised by the new round of attacks given Clinton's more conciliatory tone in their debate last week.

"I am puzzled by the sudden change in tone, unless these were just brought to her attention. It makes me think that there is something tactical about her getting so exercised. The notion that somehow we are engaging in nefarious [dirty] tactics, I think, is pretty hard to swallow," he said.

The two Democrats debate again Tuesday night in Cleveland, Ohio. Ohio and Texas, along with Rhode Island and Vermont, hold primaries on March 4 that could be decisive in the Democratic race.

The latest polls show Clinton and Obama roughly tied in Texas, but that Clinton maintains a lead in Ohio.

Most estimates give Obama about 1,300 delegates at the moment, about 100 more than Clinton.  To win the Democratic Party's presidential nomination 2,025 delegates are needed.

Meanwhile, the presumed Republican nominee, Senator John McCain, also campaigned in Ohio Monday. McCain is looking to wrap up the party nomination with convincing victories a week from Tuesday that he hopes will force former Arkansas governor Mike Huckabee to quit the race.

McCain focused on his differences over the war in Iraq with the two leading Democratic presidential contenders.

"They are liberal Democrats. I am a conservative Republican. One of those differences will be about the [Iraq] strategy. And they were wrong, Senator Clinton and Senator Obama, when they said that the surge would fail. And they were wrong when they said that the political process would not move forward," he said.

McCain and his eventual Democratic opponent will have company in the general election battle later this year. Longtime consumer advocate Ralph Nader announced he will make a third bid for the White House this year as an independent candidate committed to fighting the influence of corporate lobbyists in Washington.

"When you see Washington, D.C. become corporate-occupied territory," said Nader. "Every department and agency controlled by overwhelming presence of corporate lobbyists and corporate executives in high government positions."

Nader made the announcement on NBC's Meet the Press program.

Nader won nearly three percent of the popular vote in the 2000 election and many Democrats still blame him for taking votes away from Al Gore, who narrowly lost to President Bush.

Nader ran again four years ago but drew little support.