Only three of ten leading Presidential candidates can count on base support from at least 25% of voters. The latest Rasmussen Reports national telephone poll found that 29% would definitely vote for Illinois Senator Barack Obama (D) if he is on the ballot in 2008. Twenty-eight percent (28%) would definitely vote for New York Senator Hillary Clinton (D), and 25% would definitely vote for former Tennessee Senator Fred Thompson (R). All three are in the top tier of their party’s nominating competition as measured by the Rasmussen Reports daily Presidential Tracking Poll.

Thompson’s level of base support has increased each month that he has been included in the survey.

At the other extreme, two candidates have base opposition from more than 40% of voters. Forty-six percent (46%) say they will definitely vote against Clinton and 42% will definitely vote against Delaware Senator Joe Biden (D).

Fifty-two percent (52%) of men say they will definitely vote against Clinton along with 42% of women. A separate survey found that 68% of Americans say they are willing to vote for a woman President.

Every one of the ten candidates in the poll has more people ready to definitely vote against them than for them.

On a net basis, the top candidates are Obama (29% for, 37% against), Thompson (25% for, 34% against), and Arizona Senator John McCain (22% for, 35% against). McCain enjoyed a big improvement compared to a month ago, but is still weaker than he was two months ago. The weakest candidates on a net basis are former Arkansas Governor Mike Huckabee (6% for, 37% against) and Biden (8% for, 42% against).

Clinton’s numbers are remarkably stable. In four straight monthly surveys, the number saying they will definitely vote for her has ranged only from 28% to 30%. The number who would definitely vote against has also stayed in a very narrow range from 46% to 48%. Clinton’s numbers are also the most partisan of all candidates--53% of Democrats say they will definitely vote for her. That’s the most partisan support enjoyed by any candidate. However, 81% of Republicans and 47% of unaffiliated voters say they’ll definitely vote against her.

While Clinton’s numbers have remained stable, Giuliani’s have consistently trended downward. In March, Giuliani was the only candidate to receive a net positive number—31% said they’d definitely vote for him while 28% were definitely voting against. His net numbers have declined each month and now 22% way they’ll definitely vote for him while 39% will definitely vote against.

Still, 42% of Republicans say they’d definitely vote for Giuliani if he’s on the 2008 ballot. Forty-one percent (41%) of Republicans say the same about Thompson and 37% will definitely vote for McCain. Only 30% of Republicans will definitely vote for Romney.