The remaining U.S. presidential candidates are preparing for a major showdown on Tuesday when more than 20 states hold primaries or caucuses to choose delegates to the Republican and Democratic nominating conventions later this year.  VOA National correspondent Jim Malone has more on what the political experts call Super Tuesday.

The February 5 primaries and caucuses around the country loom as a decisive day in the battles for the Democratic and Republican presidential nominations.

In their latest debate in California, Democratic contenders Barack Obama and Hillary Clinton were noticeably nicer to one another compared to the previous encounter in South Carolina where both candidates attacked each other with abandon.

OBAMA:  "I was friends with Hillary Clinton before we started this campaign.  I will be friends with Hillary Clinton after this campaign is over."

CLINTON:  "The differences between Barack and I pale in comparison to the differences we have with the Republicans."

A total of 22 states hold Democratic primaries or caucuses Tuesday with more than 1,600 delegates at stake.

To win the Democratic nomination, a candidate must win the support of 2025 delegates at the national nominating convention in Denver, Colorado, in late August.

In the Republican race, Senator John McCain of Arizona heads into Super Tuesday as the clear frontrunner, hoping to put more distance between himself and challengers Mitt Romney, Mike Huckabee and Ron Paul.

McCain continues to emphasize his early backing for the U.S. troop surge in Iraq, which has improved the security situation there.

"Iraq is the central battleground in the struggle against al-Qaida, and if we had done what the Democrats wanted us to do six months ago, and that is to declare a withdrawal and leave, we would be fighting all over the Middle East, we would see chaos and genocide in the region," he said.

Romney argues that he is the only true conservative remaining in the Republican field.

McCain continues to come under fire from conservative activists for past stands against tax cuts and for comprehensive immigration reform.

Among his critics is the conservative radio talk show host, Rush Limbaugh.

"He is not the choice of conservatives, as opposed to the choice of the Republican establishment," he said.

The Republican contenders will compete in 21 primary or caucus events on Tuesday with more than 1,000 party delegates at stake.  A total of 1,191 delegates are needed to secure the Republican nomination.

Among those states holding primaries in both parties on Tuesday are California, New York, Illinois and New Jersey.  Smaller states in all regions of the country are also taking part.

Democratic political strategist Tad Devine predicts the Republican race will probably be decided before the Democratic contest between Clinton and Obama.

"In the Republican process, somebody, most likely McCain, will pull way ahead and the other challengers simply will not be in a position to catch him," he noted.  "That is not going to happen in our [Democratic] Party.  We are going to have a close contest that proceeds probably through the month of February into early March."

Most of the Republican contests are winner take all events, which award all the delegates at stake in a given primary or caucus to the winner.

Democratic delegates are awarded on a proportional basis, meaning even the second place candidate can win some delegates based on the proportion of the vote won in a primary or caucus.