Tuesday is looming as a critical day in the U.S. presidential campaign when more than 20 states hold party nominating contests. The latest polls contain good news for Democrat Barack Obama and Republican John McCain. VOA National Correspondent Jim Malone has a preview of the so-called Super Tuesday primaries and caucuses.

Sen. Barack Obama applauds the crowd before delivering a campaign speech in Denver, Colorado, 30 Jan 2008

Senator Hillary Clinton and Senator Barak Obama will do battle in 22 Democratic contests around the country, including states with large numbers of delegates like California, New York and New Jersey.

The latest national public opinion polls show Obama gaining on Clinton and the race nearly even. But Clinton continues to hold narrow leads over Obama in most of the larger states voting on Tuesday.

Both candidates are relying on a last minute barrage of television ads and quick campaign visits to key states to urge their supporters to vote Tuesday.

Obama cast himself as the agent of change at a rally in Delaware.

"I can offer a clear and clean break from the failed policies of George W. Bush," he said. "I will not have to explain my votes in the past."

Sen. Hillary Rodham Clinton conducts a roundtable discussion at the Yale Child Study Center in New Haven, Connecticut, 4 Feb 2008

Clinton urged voters to consider her experience during a campaign stop in Missouri.

"My opponent has not had to go through that kind of baptism by fire," she said. "Let us not kid ourselves here. This is going to be open season once again, and we need to nominate somebody with the experience and fortitude and know-how to take whatever they send our way and send it right back."

More than 1,600 Democratic delegates are at stake Tuesday, 2,025 delegates are required to win the Democratic nomination.

In the Republican race, 21 states are holding nominating contests Tuesday.

Sen. John McCain speaks at a campaign rally in Chesterfield, Missouri, 1 Feb 2008

Senator John McCain is looking to build on the momentum generated by his wins in the two most recent primaries in Florida and South Carolina.

McCain campaigned Monday in Massachusetts and sought to appeal to both Republicans and independent voters.

"As President of the United States, I will preserve my proud, conservative Republican credentials, but I will reach across the aisle to the Democrats and work together for the good of this country," he said. "That is what you want us to do, is work for the good of this country."

Mitt Romney shakes hands during a campaign stop in Nashville, Tennessee, 4 Feb 2008

McCain is trying to fend off a challenge from former Massachusetts governor Mitt Romney. Romney contends McCain is not conservative enough to be the Republican Party's presidential nominee.

"There is that old saying that if there is a race between a Republican acting like a Democrat and a Democrat, the Democrat always wins," he said.

Former Arkansas governor Mike Huckabee hopes to do well in some of the southern primaries, while Texas Congressman Ron Paul is looking for a strong showing in Alaska.

Mike Huckabee campaigns in Chattanooga, Tennessee, 4 Feb. 2008

More than 1,000 Republican delegates are at stake on Tuesday. A total of 1,191 delegates are required to win the Republican nomination.

Most political experts predict that the Democratic contest will go on well after the Super Tuesday results.

The Democrats use a method of proportional representation to award delegates from the primaries and caucuses, while Republicans generally follow the rule of winner-take-all.

"The number of [Democratic] delegates is large, but they are going to be split in a certain way, so that we will have to go on," said John Fortier, who monitors the election campaign at the American Enterprise Institute in Washington and was a guest on VOA's Encounter program. "But it could be that we could have a clear frontrunner, and I think that is more likely on the Republican side these days. John McCain, I think, has the ability or the prospect of really establishing himself as the clear frontrunner on Super Tuesday."

Looking ahead to the next major contests on the campaign calendar, Maryland and Virginia vote on February 12 while Ohio and Texas hold primaries March 4.