Start with the substance of change each offers. Democratic strategists know Mr. Obama possesses a huge vulnerability here. America is a center-right country. According to the latest Rasmussen poll, only 25 percent of voters describe themselves as "liberal." And based on the same Rasmussen surveys, 67 percent believe Mr. Obama is a liberal. By way of comparison, only 53 percent viewed John Kerry as a liberal at the end of the 2004 campaign. It's hard to imagine a center-right country - once voters focus on the candidates' ideology - will elect a person who nearly seven out of 10 believe is a liberal.Mr. Obama's voting record in the U.S. Senate supports the liberal label. Democratic Rep. David Boren of Oklahoma told the Associated Press this week that Obama was "the most liberal senator," and that his voting record in the Senate "does not reflect working in a bipartisan fashion." A growing number of Americans see it that way, too. Only 47 percent viewed Mr. Obama as a liberal in December, according to the same Rasmussen surveys referenced above - meaning a 20-point climb in just five months. That reality is like fingers scratching a blackboard for the Illinois senator's partisans.