OBAMA: Campaign holds media call to highlight strengths of Obama's tax plan.
Former Treasury Secretary Summers says Obama is more fiscally responsible than McCain and will prompt stronger economic growth.
MCCAIN: Economics aides Fiorina retorts there are "stark differences between the reality of (Obama's) record and his rhetoric" on taxes.
Says she is "mystified" by Obama's claim he would lower taxes more than McCain. "Barack Obama can say it, but it doesn't make it true."
