PRINCETON, NJ -- When Americans are asked which of the leading candidates left in the race for president they least want to see elected president this year, 40% name John McCain, 36% Hillary Clinton, and 20% Barack Obama.

McCain leads this inauspicious list in part because he is the only Republican among the three candidates -- meaning he is the primary focus of Democrats and independents who lean Democratic, while Republicans can split their choices between Obama and Clinton.

Seventy-one percent of Democrats name McCain. Republicans divide their answers between the two Democratic candidates, although they name Clinton by nearly 2-to-1 over Obama, 60% vs. 34%.

Why?

A follow-up question asking respondents for the reasons they least want to see their named candidate elected finds the overwhelming criticism of Obama is his lack of experience. The main rationale for spurning a Clinton presidency is the perception that she is untrustworthy, while the knocks against McCain are threefold: his associations with the Iraq war, with President George W. Bush, and with the Republican Party.

Obama: "Not Qualified"

Nearly 4 in 10 of those who least want to see Obama elected (39%) say they believe he is "inexperienced" or "not qualified" to be president. All other explanations are much less frequently mentioned. The reason cited second most frequently is trustworthiness, mentioned by 15% of those opposed to his becoming president. However, nearly as prevalent (12%) as an explanation for not wanting Obama elected is the belief that he is a Muslim. (Obama himself has said this is incorrect, and he is a member of the Chicago-based Trinity United Church of Christ.)

An additional 8% of Obama's detractors say they dislike his "religious affiliation," but it is unclear whether this is a reference to perceptions about Obama's connection to the Muslim religion, or to his ties to the Rev. Jeremiah Wright and Trinity United Church of Christ.

McCain: Iraq, Bush, and the GOP

Those who least want to see McCain elected president are most likely to cite his position on the Iraq war (27%), his similarity with President Bush (25%), or the fact that he is a Republican (23%). In line with these policy-oriented reasons for opposing him, an additional 8% say they "disagree with his views on most issues."

Although McCain's advanced age has been raised as a possible liability for his candidacy, only 7% of those most opposed to him say they think he's too old. Only 2% mention McCain's well-known temper management issues.

Clinton: Don't Trust Her, Reservations About Bill, and Likability

The most prominent reason given by those opposed to Clinton being elected president is not trusting her -- mentioned by 24%. However, the 18% saying they don't want Bill Clinton back in the White House and the 16% saying they don't like Hillary Clinton rank a fairly close second and third, respectively.

The 12% saying they think Clinton lacks the experience to be president is relatively small compared to the 39% saying this of Obama, but it is still more than a trivial issue for her. Half as many (6%) say the country is not ready for a woman to be president and only 2% cite her healthcare plan.

Bottom Line

The responses give an interesting initial indication of the potential vulnerabilities of these candidates in the general election. There is a notable difference in the negative perceptions of the candidates held by those most opposed to each one becoming president. The most prevalent criticisms leveled against Obama and Clinton are all personal in nature: trustworthiness, likability, experience, and family connections. By contrast, the top criticisms of McCain are all more policy oriented: Iraq, associations with Bush, and being a Republican.

Survey Methods

Results are based on telephone interviews with 1,005 national adults, aged 18 and older, conducted March 24-27, 2008. Respondents were randomly drawn from Gallup's nationally representative household panel, which was originally recruited through random selection methods. The final sample is weighted so it is representative of U.S. adults nationwide.

For results based on the total sample of national adults, one can say with 95% confidence that the margin of sampling error is ±4 percentage points.

In addition to sampling error, question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.