The Wall Street Journal reports on Nielsen’s ratings of the presidential videos on YouTube:

Traffic on YouTube related to the 2008 presidential race spiked in March and April, largely on two unofficial, critical videos, one about Democratic front-runner Hillary Clinton, the other about Republican John McCain, according to a study of YouTube traffic by Nielsen/Net Ratings.

An anti-Clinton “1984″ video, in which the New York senator is portrayed as a Big Brother-ish figure, accounted for about 75% of all traffic to candidate-related videos on YouTube in March, Nielsen found.

A month later, a video of Mr. McCain, the Arizona senator, joking about bombing Iran to the tune of the Beach Boys classic “Barbara Ann,” helped him attract more than twice as many visitors on YouTube than his Republican rivals.

While overall viewership of political videos is relatively small, the clips are becoming increasingly important in the elongated 2008 presidential campaign cycle. Lesser-known candidates are using YouTube as a low-cost method to get some attention, while the leading candidates are trying to avoid any embarrassing on-the-trail goofs that can be exploited by opponents or their supporters.

This early in the election cycle, it’s hard to say that Internet volume at candidate Web sites is an indicator of ultimate success at the polls. If anything, the data show that the increasing attention being placed on the Internet by candidates is a double-edged sword, since they are getting the most attention online for video clips beyond their control.

They acknowledge that Clinton’s pick-my-song videos also caused a spike. Apart from those spikes, Nielsen says, traffic to the Republicans and Democrats is each running at 300-400,000 unique users a month.

Another question that hasn’t been answered is whether and how these videos — positive and negative, campaign-controlled and independent — are affecting voters’ views . . . and media coverage. In short: What is the impact of the YouTube campaign? I’d like to see some qualitative research on this, please.