Liberal use of the phrase "Most Liberal"

When Al Gore ran for President he was portrayed by the Republicans as the most liberal member of Congress. When it was John Kerry's turn at bat, the same claim was made.

Now:

National Journal has ranked Sen. Barack Obama as the most liberal member of the Senate. Sen. Hillary Clinton ranked 16th.

Is it just coincidence that the current Democratic Presidential candidate gets this honor, or is this a "scare" tactic the conservatives use to motivate fear of the opposition? Is that a rhetorical question?