Well it came from a
single survey in the National Journal which looked at a single year of voting (2003) and which only included votes handpicked by National Journal editors.
Some points from the linked article follow
National Journal's vote ratings rank members of Congress on how they vote relative to each other on a conservative-to-liberal scale in each chamber. The scores, which have been compiled each year since 1981, are based on lawmakers' votes in three areas: economic policy, social policy, and foreign policy. The scores are determined by a computer-assisted calculation that ranks members from one end of the ideological spectrum to the other, based on key votes -- 62 in the Senate in 2003 -- selected by National Journal reporters and editors.
The fact that Kerry and Edwards had such similar scores in 2003 is striking, because during the course of their Senate careers, their ratings have often placed them in different wings of their party.
[snip]
Kerry has compiled a generally more liberal voting record. After winning election to the Senate in 1984, he ranked among the most-liberal senators during three years of his first term, according to National Journal's vote ratings. In those years -- 1986, 1988, and 1990 -- Kerry did not vote with Senate conservatives a single time out of the total of 138 votes used to prepare those ratings.
Edwards, on the other hand, had a moderate voting record during the first four years following his election to the Senate in 1998. The results positioned Edwards comfortably apart from Senate liberals, but not so far to the right that he locked arms with centrist Republicans. His consistent moderation placed Edwards among the center-right of Senate Democrats. But once Edwards decided to run for president and abandoned his bid for a second Senate term, his record moved dramatically to the left in 2003.
Last year, Kerry, Edwards, and other congressional Democrats who were seeking the presidency, including Sen. Joe Lieberman of Connecticut and Rep. Dick Gephardt of Missouri, missed many votes. To qualify for a score in National Journal's vote ratings, members must participate in at least half of the votes in an issue category. Of the 62 Senate votes used to compute the 2003 ratings, Kerry was absent for 37 votes and Edwards missed 22.
As a result, in the 2003 vote ratings, Kerry received a rating only in the economic policy category, earning a perfect liberal score. Edwards received ratings in the categories of economic and social issues, also putting up perfect liberal scores.
[snip]
To be sure, Kerry's ranking as the No. 1 Senate liberal in 2003 -- and his earning of similar honors three times during his first term, from 1985 to 1990 -- will probably have opposition researchers licking their chops. As shown in the accompanying chart, Kerry had a perfect liberal rating on social issues during 10 of the 18 years in which he received a score, meaning that he did not side with conservatives on a single vote in those years. That included his 1996 vote, with 13 other Senate Democrats, against the Defense of Marriage Act, which prohibited federal recognition of states' same-sex marriage laws. Along the campaign trail, Republicans likely will remind voters of Kerry's stance on that issue.
But interestingly, during Kerry's second term, from 1991 to 1996, he dropped back into the pack of Democratic senators and voted more moderately. In those years, he earned composite liberal scores in National Journal's vote ratings ranging from 78.2 to 85.8.
Kerry was especially moderate in his second term when it came to foreign-policy issues. He opposed the liberal position in key Senate showdowns on missile-defense and intelligence spending in 1993, and on procurement of additional F-18 Navy fighters in 1996. Such votes could provide Kerry with some useful talking points for his presidential campaign. Kerry also voted with President Clinton and congressional Republicans, but against many liberals, in favor of welfare reform in 1996, and he occasionally split from organized labor on workplace issues.
While I do not think Kerry or Edwards should necessarily run away from the liberal label (I mean, look what nearly 4 years of "compassionate conservatism" has given us. How could liberals be any worse), I think the GOP labeling of the ticket as the "most liberal ever" is quite a stretch. It's not a surprise, but it would be nice if someone in the SCLM would call them on their truth-bending.
I guess the upside of all this GOP noise, is that if this garbage is the best they can drum up against Kerry/Edwards, we are in good shape.