A Univision debate is postponed because Sen. John McCain is the only top tier candidate who agreed to participate.

McCain, former New York mayor Rudy Giuliani and Gov. Mitt Romney are asked questions at a Values Voter Presidential Debate in Florida -- questions that go unanswered because none of them are there.

And tonight, Tavis Smiley will moderate a Republican debate at a historically black college in Baltimore. All four GOP presidential front-runners -- Giuliani, McCain, Romney and former Tennessee Sen. Fred Thompson -- have said they are not coming, citing scheduling conflicts and fundraising pressures.

To some voters, skipping debates may seem like the ultimate snub toward whoever organized the event. But the decision to participate in a debate or stay home is much more complex than that, according to several political experts.

Take the Romney campaign, which says there are many factors they consider when the decision is being made. For example, according to campaign spokesman Kevin Madden: where the debate is taking place.

"Obviously states where early primaries are being held become a priority at this point in the campaign," he wrote in an e-mail.

He added that the campaign has had to decline several debate invitations at the end of September because "travel demands related to fundraising" -- the fundraising quarter ends Sept. 30.

"Even the best debate performance will go unnoticed if a campaign reports a slow fundraising quarter only a few days or even a week later," he said.

asap spoke to several political scientists and consultants to learn more about why candidates are sitting some of these debates out.

___

FEW VOTES TO BE HAD

The African-American vote is solidly in the Democratic corner, says Steffen Schmidt, a political science professor from Iowa State. In fact, the percentage of African-Americans who consider themselves Republican hovers around 9 percent.

"From a pragmatic point of view, there aren't going to be many African-American voters who are going to vote for a Republican presidential candidate," says Schmidt. "It is not of much importance for Republicans to spend their time and money attending African-American forums."

___

RISKY BUSINESS

For candidates, fewer debates are better than more, says Kathleen Dolan, a political science professor at the University of Wisconsin-Milwaukee.

Minimizing debate appearances means fewer chances for the candidate to mess up -- rile the audience, stumble over a question, inadvertently offend the audience, like presidential candidate Ross Perot did when he referred to blacks as "you people."

"If Republicans took part in that Spanish language debate, they are going to get hammered on immigration for two hours," she says. "If they speak to African-Americans, they're going to have to talk about affirmative action -- all types of stuff for which they don't agree with most of the audience."

___

TOO MUCH TOO SOON

Some of this skipping is also the result of an unprecedented number of debates this early in a campaign season, says Dolan.

There's been a big increase in the number of debates sponsored by "interest groups," such as the AFL-CIO labor federation or Univision, that target segmented audiences -- as opposed to traditional debates that are sponsored by state political parties, she says.

"From the candidate's perspective, being tied down to that many debates is problematic," says Dolan. "The candidates want to campaign in certain places -- in the early primary/caucus states and where their money builders are."

___

TOO MANY CANDIDATES!

The presidential race is crowded, with 10 Republican candidates and eight Democratic ones, which means shorter sound bites, less face time and more statements than actual debate, says Gary L. Rose, professor of politics at Sacred Heart University in Connecticut.

"Each candidate gets a limited time to make a prepared statement," he says. "Even if it's still off the cuff, it's short and doesn't allow the other candidate to cross-examine the position."

Former Republican political consultant J. David Woodard, who teaches political science at Clemson, says a GOP debate he attended was like a carnival.

"Twelve people up there all trying to say something, none of them really able to do it," he says. "It's just really hard to distinguish yourself."

___

CANDIDATE SEE, CANDIDATE DO

For the second-tier candidates, there's almost no downside to participating in a debate -- they need all the exposure they can get.

Among the front-runners, though, the risks of a debate simply aren't worth it if the other front-runners aren't there too. So when one front tier candidate declines to participate, the others may follow.

"If Giuliani and Thompson aren't there, then why does Romney want to show up?" asks Philip Klinkner, professor of government at Hamilton College. "It's not going to gain you anything. You may lose to Mike Huckabee."

___

AGAINST THEIR BELIEFS

GOP candidate U.S. Rep. Tom Tancredo wants to crack down on illegal immigrants. He has crusaded against bilingual education. Participating in a Spanish-language debate, where the organizers feel otherwise, may simply go against his beliefs.

Meanwhile, some Democrats accuse Fox News of being biased toward Republicans and conservatives, so the Democratic front-runners have refused to participate in Fox-sponsored debates.

___

TOO MUCH TIME

No, we're not talking about the time spent traveling and the hour or two on television, says Kiki McLean, who was press secretary for Al Gore's presidential campaign.

Debates, she says, are long-term investments of a candidate's time -- policy research, practicing answers, learning how to react to the competition's statements.

Some candidates feel their time could be better spent elsewhere.

"They have to weigh it," says Woodard. "'Is it better for me to go out and raise money or go to this debate?' I think some have decided, 'My strategy will be better if I go ahead and do something else.'"

___

Megan Scott is an asap reporter based in New York. Raghu Vadarevu also contributed to this report.

___

Want to comment? Sound off at soundoffasap@ap.org.